Agri-drinking water quality indicators and IT/sensor techniques

Science

Main authors:	Susanne Klages, Nicolas Surdyk, Christophoros Christophoridis, Birgitte Hansen, Claudia Heidecke, Abel Henriot, Hyojin Kim, Sonja Schimmelpfennig
FAIRWAYiS Editor:	Jane Brandt
Source document:	»Klages, S. et al. 2018. Review report of Agri-Drinking Water quality Indicators and IT/sensor techniques, on farm level, study site and drinking water source. FAIRWAY Project Deliverable 3.1, 180 pp

Contents table
1. Definition based on literature review
2. What can we expect from monitoring?
3. Participative monitoring in FAIRWAY

1. Definition based on literature review

“Citizen science”

For many researchers, participative monitoring is a subset of citizen science that focuses on repeated data collection by non-scientists, often dedicated to identifying trends over time (Etrella and Gaventa, 1998). Although some researchers might disagree with that point of view, this categorization will be used (Eitzel et al., 2017, Lovett et al. 2007). Many definitions have been proposed for “citizen science”. One of the first attempt was in 1995 to describe expertise that exists among those who are traditionally seen as ‘lay people’ (Irwin, 1995). It is one of the broader applications of the term. The term citizen science was added recently to the Oxford English Dictionary in 2014 as:

“Scientific work undertaken by members of the general public, often in collaboration with or under the direction of professional scientists and scientific institutions.”

The main tenet of this concept is that members of the public are involved in science as researchers (Conrad, 2011). In order to extend this term to wider public than ‘citizen’ (which may imply a narrower definition, of a native or naturalised member of a state or nation), various terms were proposed: “community science” (Conrad, 2011), and Public Participation in Scientific Research” (PPSR) or “citizen and community science” (Eitzel et al., 2017).

In Europe, scientists as professionals is relatively new, emerging slowly throughout the 17th to 19th centuries, with specialization in science. Consequently, the distinction between “scientists” and “citizen scientists” is also relatively new. ‘Citizen scientist’ (meaning scientist independent of institutions) was used at least as early as 1912 (Eitzel et al., 2017). Before, the word “participative monitoring” was establish, the use of “unprofessional” collaborator was common. Many institutions asked vessel captains or crew medical officers to collect plants in newly discovered territory through the 16th and 17th centuries.

The participation of the public/citizens in science decreased during the 19th to 20th centuries with the increase of science specialisation. However, during the second half of the 20th century, thanks to technology development, citizens participations increased again. The fields in which citizen science is used are diverse: ecology, astronomy, medicine and much more. The point of a citizen science project is to facilitate scientist and citizen to collaborate towards a common goal. The collaboration that can occur through citizen science allows investigations at large scales and long time, that can lead to discovery scientists could not have achieved on their own.

Citizen scientists can help with opportunistic and observational studies that do not follow a strict design. These studies can be useful because of the large temporal or geographic scale of the data collection, the rarity of the phenomena observed (e.g., a rare species or infrequent weather event), or the timeliness of the observations (e.g., collecting information for crisis response, such as after earthquakes or oil spills), all of which make data collection difficult (McKinley et al., 2017).

Citizen scientist can participate in various ways in citizen science program by, 1) proposing programs, 2) analysing data and 3) collecting data. The last aspect (collecting data) is what refered to as “Participatory monitoring”.

Participative monitoring

Citizen observation of the environment and collection of data is a very ancient practice, being undertaken informallybefore the definitions of citizen science and citizen scientist were coined. But this practice, gradually fade until the 20th century, because the means of data collection was out of reach of many.

It was through association networks (e. g. Nature Conservatory, Earthwatch) that the practice of observing nature maintained its momentum in the second half of the 20th century. In the 1970s, some associations for the protection of birds used citizen science to developed programs of birds watching. Other citizen observation programs quickly follow in the course of the 1990s, involving mostly passionate, professional and amateur naturalists (Conrad and Hilchey, 2011). But, it was not until the 2000s with the advent of the internet, that the movement significantly accelerated and, above all, became open to a much wider audience.

Citizen observations of the environment today, covers a wide range of concerns. The quality of the environment, noise, air pollution, or even the quality of the water have become major concerns for citizens and new tools have faciliatitated their greater involved in address these issues. Technology developments have played an important role: the widespread use of smartphones and the ability to produce pollution sensors at a (relatively) low cost opened new horizons for citizen observation of the environment.

The notion of “participative monitoring” has several aspects in literature. As for "citizen science”, various definition are used such as “community based monitoring” (CBM). This expression includes a diversity of projects that involve citizen groups more or less organised in a collective observation and monitoring process of the environment (Conrad and Hilchey, 2011). More recently, participative monitoring programs have also included an increase of public education (Brossard et al., 2005) and/or an increase of the citizen’s involvement in the environmental decision linked to a specific project. Participative monitoring in its most inclusive form should include stakeholders in decision making but does not always do so even if volunteers tend to have the hope that their efforts will be used to assist in local decision making (Conrad and Daoust, 2008).

Participative projects have several characteristics, including the type of environment observed; the type of public mobilised and the program management. In the FAIRWAY project, we will focus on participative monitoring in a context of a scientific project, in the context of local/regional issue monitoring program.

Scientific project monitoring program: Scientific project monitoring programs have, as a principal characteristic, the generation of scientific knowledge. They either mobilise a well informed public, able to carry out a rigorous or data protoccols or or else citizens who have been trained to collect data according to the protocol.

These projects are usually driven by one or more research laboratories, often at the national level but also at local scale, and in partnership sometimes with associations or local organisations. Most of the large-scale ecosystem monitoring programs (e. g. bird monitoring programs) tend to be collaborative.

In the field of the environment, collaborative science programs are often developed around the theme of biodiversity. The Anglo-Saxon countries have generally been pioneers in this field. In Britain, for example, the Natural History Museum and the association Royal Society for the Protection of Birds have led for several decades programs of identification and monitoring of common birds by relying on a network made up of thousands of amateurs and professional naturalists (Bing et al., 2008).

The challenge is then to produce a suitable protocol that is 1) sufficiently scientifically rigorous, and 2) not too complex (and ideally enough fun) to enable broad public support.

These monitoring programs involve a central agency (most of the time a government agency or a governmentally funded agency) that requests information from volunteers. The purpose of monitoring by these volunteers is to provide early detection (by citizens) of issues of environmental concern, which can then be investigated/analysed by scientific experts (Whitelaw et al., 2003, Conrad and Daoust, 2008).

Although often successful in the short term, monitoring by volunteers are often funding dependent and cannot continue on their own without government or doner assistance. Also, these volunteers may not represent a very diverse stakeholder group as they have a vested interested in the issues being address in the monitoring program (i. e. only fishermen or only farmers; Conrad and Hilchey, 2011).

In most of the projects, the general principle is to rely on a network of volunteers (citizens) to follow a protocol of data collection with a scientific purpose. Most of the time, a website acts as an interface between scientists and the volunteers. The volunteers have to be able to recognise, count and locate individuals (animals or plants for example), with lots of information being downloaded from internet. Then they enter their comments on a website, the information is then sent directly to the researchers. The findings of the research are generally published on the same website, to inform citizen observers of the findings of the program (Figure 11.1).

D3.1 fig11.01
Figure 11.1

Local/regional activism monitoring programs: This type of programs often focus on local issues for which actions by governments should be initiated but has not occurred (Conrad and Daoust, 2008). It often focusses on specific issues and sometimes has no private sector or government support (Whitelaw et al., 2003). These participative monitoring projects are characterised by perspectives of joint public action. For these projects, the scientific goal is that data is generated that will inform local citizen to take action on a specific issue.

The general principle of this type of participative monitoring is to mobilise a network of highly motivated volunteers, to collect data. They supply data to an organisation to develop an action program or intervention. As a result, the project manager is rarely a research laboratory, but more often an organisation (administration or association, for example) who seeks to deal with a problem in a given territory. Such programs can for example provide comments on the invasive species or allergens in order to deploy a program to fight against their dispersion or it can aim to develop an inventory in order to fight against a project planning (Bing et al., 2008).

The monitoring devices used in these projects are similar to those for scientific programs. On one side, the scientists (belonging to an administration or association for example) develop the data collection protocol. On the other side, volunteers collect data using the protocols and equipment supplied by the scientists. Volunteers provide their observations to scientists, directly, or through a website that allows the data entry. These data are then compiled and can lead to concrete action (plan of action, mobilisation, etc.; Figure 11.2).

D3.1 fig11.02
Figure 11.2

In some of this “bottom-up” monitoring programs, the local communities do not trust the data provided by the private companies and/or government organsiations and want to acquire data by themselves. In many instances,”official” monitoring programs also exist, which may have a high degree of technical credibility, yet generate little credit for the community (World Bank, 2008).

One reason for this is that most monitoring programs are top-down, with the public receiving information that has been collected, analysed, and reported by experts chosen by the project sponsor or company and presented in a way that the public may not understand. In many instances, the information may not even address the real concerns of the community; rather, it may be strictly oriented toward a organisation self interests in relation to compliance with regulations and legal commitments (also an important function of monitoring) (World Bank, 2008).

However, many failures of bottom-up community based monitoring groups are mentioned. These include lack of success due to little organisation credibility and capacity (Bradshaw, 2003). Others suggest that bottom-up participative monitoring programs tend to be unsuccessful on a more organisational level, perhaps due to poor goverance structures and no legislation or policy support (Conrad and Daoust, 2008).

Global concern monitoring program: The emergence of measurements carried out directly by citizens in open mode and using mobile technologies are gradually taking the shape of networks of “human sensors”. This category of participative monitoring includes devices geared towards the general public.

They fit into a perspective of democratisation of the tools for environmental monitoring and are present as complementary to official measures devices (alternative monitoring) to feed and eventually guide public policy. Moreover, they are mostly in the field of "low-dose", i. e. low impact/frequency pollution (pollution of air, water, sound), which they aim to measure and understand for a better control.

These devices provide the ability to have a global networks of sensors, their strength beingin the mass production of environmental data. Also, unlike the participative monitoring of "scientific program" or “local issue monitoring program”, this type of participative monitoring is little governed by a scientific protocol (which is based on the formulation and testing of hypotheses). They fit into a perspective of democratisation of the tools of environmental monitoring and present themselves as complementary to official measure devices (alternative monitoring) to feed and eventually guide public policy.

The results of measures are data visualisation tool and maps with with generaly little corrections or caculations between the measures and the maps/visualisations. The tools to visualise the measure repartition is generaly provide with the tools to collect the data (Figure 11.3).

D3.1 fig11.03
Figure 11.3

The complementarity of these devices with those of public administrations is based on two key principles:

the multiplication of the number of sensors/observers may support a measure based on a limited number of institutional sensors (e. g. sensors payed by government),
the production of measures of exposure for individuals rather than exposure based on a ‘representitive’ place: participants measure precisely what pollutants they are exposed to in their daily lives.

Issues for “human sensor” monitoring arise during data collection. These include data fragmentation, data inaccuracy, and lack of participant objectivity (Whitelaw et al., 2003). Studies are often lacking in experimental design and do not consider issues such as adequate sample size (through a priori power analysis, for example). This could generate mistrust (by the scientific or government community) in the credibility and capacity of “human sensor” monitoring data (Conrad, 2007).

2. What can we expect from monitoring?

Increase cost benefits of action

A key benefit of Participative Monitoring programs is a decrease in the cost of official (i. e. governmentally funded) monitoring programs (almost uniquely) in the field of research.

The general decrease in prices of connected tools and the increases of on-line tool are the main drivers behind the recent success of citizen science and participative monitoring programs. However, this is also the case for more ‘classic’ type monitoring programs. Two decades ago, groundwater level was computed manually every few days whereas now hourly data can be downloaded automatically on a central database. Innovative connected tools (a connected tool received instructions or parameters from the backend, and/or sends to this backend data points collected by its sensors) are not only present in the smartphone field but also in the field of conventional sensors (hourly measurement and hourly transmission are technically achievable and economicaly accessible).

Connected tools (automated probes) and participatives monitoring have different benefits. Automated approaches have the benefit of regular and frequent (e. g. daily or hourly) measurements whereas the participative monitoring has benefits that counterbalance the lower data frequency, such as engage volunteers and encourage them to become interested in local water resources. Anyhow, the costs are not necessarly lower (Little et al, 2016).

Participative monitoring seems to be a great solution in specific research programs where scientists do not want to (or cannot) spend time or money to realise a task. This kind of monitoring could be valuable in large countries or for monitoring in remote area. In Europe, several network (Lora, GPRS) can be used, so connected tools can be used instead of participative monitoring, and the issue is more a matter of costs than a matter of technical devices.

Modification of volunteers behaviour

Many monitoring programs rely on the idea that making people participate will make them more interested in the topic and more generally in science. However, if specific education and training actions are not planned in the project, the increase of interest is generally marginal as volunteers are usually already interested and motivated individualls people.

Increases of knowledge in a specific domain has been observed in some participative monitoring projects (bird watching) but in other programs the volunteers did not really understand what they measured and misunderstood the results (Land-Zandstra et al., 2016).

In fact, to improve the quality of their data (or increase the reception of their paper in a peer-review journal), the tasks asked to volunteers are generally very simple and do not improve their scientific knowledge. Only teaching and direct contact with scientists has been shown to increase participants general knowledge, and so monitoring activities alone cannot fulfill the hopes of increasing public knowledge. Where it is essential to increase environmental awareness, other more suitable and efficient methods. like environmental education, can be used to reach this goal (Garcia and Lescuyer, 2008).

Participatory methodologies in the agricultural sciences usually involve limited numbers of farmers, working in collaboration with researchers, and scaling is usually difficult when the aim is to reach a number of larger farmer groups (Beza et al, 2017). The selected farmers (the initial volunteer group) are already conscious of their dependence on their natural resources and are generally willing to change their practices (Dangles et al, 2010). In monitoring, there is no guarantee of environmental efficacy even if the monitoring phase is a success; research message is transfered to farmers who have the role of the adopters or rejectors of innovations developed by others (Probst et al., 2003).

Some of the stakeholders, as well as many farmers do not want to be volunteers because they see monitoring as a way to impose on them new ecological constraints.

Increase administrative action

Because of the common mistrust of public against private companies and government funded monitoring programs and vice versa, the administration mistrust of participative monitoring, monitoring not supervised by administration is rarely used outside of the research world.

Data quality is almost universally recognised as one of the problems that scientists working in case studies need to address (Riesh and Potter, 2014). For example, some studies have shown that monitoring based on visual counting approaches need to take into account specific risks of bias due to the technique itself, volunteers' competences (Crall et al, 2011), the sampling effort and volunteers' missing impartiality (Leopold et al, 2009).

Citizen science and participative monitoring has led to an important number of scientific publications but yet only few administrative decisions (Yank, 2005).

Examples of participative monitoring programs

The examples below are existing (or previously existing) programs that have reached a broad audience. The projects presented here are mostly from North America because a selection was made on the availability of accessible websites. The selection was also made to present an aspect as wide as possible of different projects on the water. Direct measurement programs for nitrates or pesticides are nevertheless rare.

CATTFish The CATTFish, which stands for Conductivity and Temperature in your Toilet, uses an instrument that measures conductivity in water, allowing citizen in the US to monitor the quality of the water inside their home. It is designed with sensors that sit in a toilet tank. With a push of a button, it takes a measurement each time the tank refills after a flush. The main aim of this program is to measure a potential impact of hydraulic fracturing (www.environmentalhealthproject.org).

Rhode Island Water Quality Measure Program The heart of the program consists of weekly measurements of water quality taken by numerous trained volunteers. The program emphasises watershed scale monitoring, because the water quality of a given body of water is a reflection of the activities in the lands and waters that surround it and lie upstream. The program encourages citizen to understand the need to cooperatively manage and improve the water quality of water bodies within a watershed. In the program, the most common measured parameters are: water clarity, algal density, dissolved oxygen, water temperature, alkalinity and pH (https://web.uri.edu/watershedwatch/program-information/).

Streamselfie and Stream Tracker These two programs have the same objective: building of a map of a stream using photographs taken by volunteers. In Streamselfie, the aim of the map is to improved stream monitoring so community organisations involved in water monitoring are also part of the projet. The program aims at highlighting streams that are being monitored recently/at present and at developing a national inventory of streams that need to be monitored (http://www.streamselfie.org/). Stream Tracker aims at the improvement of mapping and monitoring smaller, intermittent streams through crowd sourced on-the-ground observations of streamflow presence and absence. Stream Tracker aims at filling in this information gap by combining a network of citizen scientists, sensors, and satellite imagery to track when and where streams flow (http://streamtracker.org).

NECi's Handheld Photometer The handheld photometers send nitrate and phosphate data to mobile phones when used with enzyme-based test kits. This tool can be used to obtain accurate nitrate or phosphate concentration in water, soil or plant tissue samples. The enzyme-based test kits provide reliable results while the photometer design ensures accurate translation of the quality data. The design of the photometer enables any citizen scientist to collect accurate nitrate data. The app software allows teams to effortlessly share results and coordinate projects with team members (http://nitrate.com/store/index.php/nitrate-phosphate-photometer).

Roaring Fork Watershed Stream Temperature Monitoring This program is based on the citizen growing concern about stream temperatures increases (with flows expected to be lower than average for instance) and its potential impact on fishes and other aquatic species. Citizen scientists will volunteer to take water temperatures in the streams and rivers throughout the Roaring Fork Watershed (in US) so they can detect unusually high temperatures (http://www.citsci.org/cwis438/websites/citsci/home.php?WebSiteID=7).

KSU "Citizen Science" The KSU "Citizen Science" program is designed to let community members do their own soil and water testing through the use of accurate test kits. Results can inform if a stream, lake, or another water supply meets water quality standards. They can also be used for the preliminary testing of drinking water, but a certified laboratory should perform follow-up testing if a problem is suspected. A helpful "how to" video for testing water in a local community or as part of a stream monitoring network is presented on the website (www.oznet.ksu.edu/kswater).

Know Your Water: Sustainable Groundwater Research The primary objective of this project, run by a group of postgraduate students, is to model the distribution of modern groundwater across South Africa. In order to achieve this goal, an isotope tracer, tritium (the radioactive isotope of hydrogen), is measured in rainfall and groundwater samples. The sampling trip involves the collection of groundwater samples from pre-determined boreholes, where one can measure the depth to water as well as setting up rainfall collection stations. Citizen scientists who have received their sampling kits in the mail will sample rainfall and their groundwater from boreholes/springs and send them back to the project team for determination of the tritium activity.

Nitrate App A Nitrate App is tested currently in the Netherlands. A reference map is necessary. Surface water and groundwater are analysed with test strips (paper based sensors). Using the App, the result can be scanned and, if desired, shared. The App is in particular designed for people working professionally with water quality such as farmers, water authorities and water companies (https://www.deltares.nl/en/news/the-nitrate-app-testing-what-you-cant-see/).

3. Participative monitoring in FAIRWAY

Evaluation of a device (tools)

Different tools (devices) that can be used for particpatory monitoring of pestcide and nitrates in groundwater and surface water, will be tested during the FAIRWAY project.

Currently in government monitoring programs, are spatially and temporal limited. Using volunteers in a participative monitoring action could increase the number of data available for a specific site (river or spring) or increase the number of points (stream, priezometer) followed.

Participative monitoring’s main interest is to gather a community around a a concept and/or an issue. In FAIRWAY, particpative monitoring will be address in two ways.

Connected probes will be used to measure directly the concentration of nitrates in soils to help farmers to better understand fertilisation impact and then better calibrate fertilisation. The probes are maintained by the farmer and they will be provide with access to a website where there will be provided with support to help with the interpretation of the results collected
Passive samplers will be evaluated for used in the measurement of pesticides (e.g. MCPA) concentrations instreams. If passive samples the evaluation demonstartes that passive samplers provide an accurate estaimate of the load of pesticides in the stream, then in the future thaey can be used to help farmers to better understand the impact of pesticides application of the drinking water quality in thier area. The management of the passive samplers during the FAIRWAY project will be done directly by farmers, as orginally hoped, but instead by other staksholders within the MAP of the specific case study catchments.
»Use of passive samplers in drinking water catchments

These approaches toparticipatory monitoring are more valid for surface water than for groundwater (except if springs are present on the catchment).

Evaluation of a method

Education is propably the best way to change stakeholder behavior, with participative monitoring providing supplementary support for this. Significant improvements in stakeholder knowledge are not be expected as a result of this element of the FAIRWAY project, as the monitoring program will not be accompanied by and eductaional program. However, some training will be provided on site to upskill stakeholder on handling the device. Unfortunately, there will be less opportunity than expected to apply participative monitoring in case studies.

Note: For full references to papers quoted in this article see

» References

Main authors:	Susanne Klages, Nicolas Surdyk, Christophoros Christophoridis, Birgitte Hansen, Claudia Heidecke, Abel Henriot, Hyojin Kim, Sonja Schimmelpfennig
FAIRWAYiS Editor:	Jane Brandt
Source document:	»Klages, S. et al. 2018. Review report of Agri-Drinking Water quality Indicators and IT/sensor techniques, on farm level, study site and drinking water source. FAIRWAY Project Deliverable 3.1, 180 pp

Contents table
1. Sensors for pesticide measurement in water
2. Sensors for nitrate measurement in water
3. Automatic sampler techniques for pesticide and nitrate measurement in (soil-) water

1. Sensors for pesticide measurement in water

Optical Sensors

Optical sensors provides a facile, rapid and low-cost approach for sensitive detection of pesticide based on FL, UVevis, Raman, SPR or chemiluminescence signal variations. Generally, an optical sensor contains recognition unit that can interact specially with desired target pesticide and transducer component that is employed for signaling the binding event. Recognition elements including enzyme, antibody, molecularly-imprinted polymers, aptamer, and host-guest recognizer, draw increasing attention of scientific researcher to improve analytical performance of sensor. By combining the recognition units-assisted target response, the current well-established optical probes can be divided into four broad categories based on signal output formats:

fluorescence (FL),
colorimetric (CL),
surface-enhanced Raman scattering (SERS),
surface plasmon resonance (SPR),
chemiluminescence.

The optical sensors for pesticide detection based on various optical detection modes are fully described in a recent review (Yan et al., 2018) and are outlined below.

Fluorescence sensing strategy: With high sensitivity and simplification, fluorescence-based sensors as one of the most commonly used sensing candidate, have been widely applied in broad fields, including environmental monitoring ((Li et al., 2016, Guo et al., 2015, Wu et al., 2014), as the signal change can be collected vis spectrofluorophotometer and observed by naked eye on-site (Paterson and de la Rica, 2015, Wu et al., 2016, Zhang et al., 2011). As the development of advancing technologies, various kinds of materials have been widely employed for the fabrication of FL sensing platform, including fluorescent dyes (Strobl et al., 2017), semiconductors nanomaterials (Wu et al., 2013), metal nanomaterials (Chen et al., 2015, Wang et al., 2017), carbon materials (Yuan et al., 2016), and rare earth materials (Li et al., 2015). Meanwhile, it is very critical to choose and design a proper recognition unit that combined with FL probe for responding the fluorescent “turn off”, “turn on”, or “ratiometric” signal. Nsibande and Forbes reviewed the development of quantum dots-based FL probe for pesticide detection in terms of enzyme, molecularly-imprinted polymers (MIPs) and host-guest recognizer (Nsibande and Forbes, 2016). On the basis of the application of recognition elements, FL sensing strategies can be typically classified into several types: enzyme-mediated methods, antibody-assisted methods, MIPsbased methods, aptamer-based methods, host-guest complexes probe and other approach (see Yan et al., 2018 for details).

Colorimetric sensing strategy: Owing to its convenience and simplicity, colorimetric (CL) sensing strategy has proven to be a powerful analytical approach for the analysis of variety of analyte, including ions (Wang et al., 2014), chemical warfare agents (Yue et al., 2016), small organic molecules (Liu et al., 2011) and biomarkers (Sun et al., 2014). A prominent merit of CL sensing is that their direct visualization output makes them promising candidates for point-of-care assays. Therefore, the key challenge for fabricating CL platform is transforming response behavior into visual color change. Reviewed the remarkable achievements of nanomaterials, AuNPs as fascinate signal transducer have been widely utilized to design CL sensors for pesticide detection. Xu et al. developed AuNPs-based probe for the directly monitoring of acetamiprid based on the strong affinity between cyano group and gold (Sun et al., 2011). The sensing mechanism was based on the state change of AuNPs from dispersion to aggregation. The concentration of acetamiprid can be qualitatively estimated from the color change (red to blue). The color change during nanoparticle aggregation is highly dependent on their distance and concentration. Chen et al. (2018) used citrate-stabilized AuNPs for the rapid detection of terbuthylazine and dimethoate by visualizing the color change. This AuNPs-based CL sensor showed high selectivity and good sensitivity for pesticide detection in real environment samples. Recently, a CL sensor array was constructed for identifying five OPs based on the dispersion-aggregation behavior of AuNPs by Fahimi-Kashani and Hormozi-Nezhad (Fahimi-Kashani and Hormozi-Nezhad, 2016). Apart from unmodified AuNPs, functionalised AuNPs have been utilized to improve selectivity for CL detection of pesticide as well. Sun et al. displayed p-amino benzenesulfonic acid functionalised AuNPs as signal reporter for detecting carbaryl (Sun et al., 2013). Based on the similar protocol, Kim et al. (2015) introduced imidazole into AuNPs-based probe to improve the sensitivity and shorten the detection time for quantitative analysis of diazinon. In addition, melamine (Liu et al., 2015), p-nitroaniline dithiocarbamate (Rohit et al., 2016) and guanidine acetic acid (Bhamore et al., 2016) were also served as ligand to decorate AuNPs for selective CL detection of pesticide. Despite many advantages of those aggregate sensors including easy-to-use and cost-effective, more endeavors are still needed to improve the sensitivity and selectivity. The combination of recognition elements is preferred as they address the above limitations. Thus, numerous efforts have been devoted to integrating the specific affinity of recognition units with the optical properties of metal nanoparticles for realizing pesticide analysis in a sensitive, selective and accurate manner. From perspective of recognition elements, CL sensing strategies can be typically summarised as four types: enzyme strategies, antibody assays, aptamer-based methods and other approaches (see Yan et al., 2018 for details).

Surface enhanced Raman scattering strategies: Raman spectroscopy can identify the chemical content of different molecular species via the collection of molecular vibrations, that is, Raman spectroscopy possess the capability of molecular “fingerprint” recognition for distinct molecule/analyte. Surface enhanced Raman scattering strategy (SERS) essentially integrated the molecular specificity of Raman spectroscopy with optical properties of plasmonic nanostructures (Gruenke et al., 2016). Owing to optical resonance properties of coinage-metal nanostructures, the local electromagnetic field can be significantly enhanced, accompanying the improvement of the SERS signal. Taking advantages of ultrafast analysis capabilities, label-free, high stability and nondestructive characterization, the application of SERS received numerous concern in the field from biomedical diagnosis to environmental monitoring (Cialla-May et al., 2017, Henry et al., 2016, Ali et al., 2016). By means of coinage-metal nanostructures, SERS can even achieve an ultra-sensitivity down to the single-molecule level, which offered new opportunities toward obtaining single molecule recognition (Ding et al., 2016, Zrimsek et al., 2017). Recently, the development of SERS technique for pesticide detection in the aspect of sensitivity, reproducibility, selectivity and portability was recently reviewed (Pang et al., 2016). The following are recent achievements in pesticide SERS strategy as a powerful analytical tool that have focused on the development of metal nanostructures-enhanced amplification. In this section, according to the coinage metal nanoparticles-based solid substrates, SERS nanoprobes are typically designed as gold substrate, silver substrate and Au@Ag bimetallic substrate (see Yan et al. 2018 for details).

Other detection strategies: Other detection techniques, such as surface plasmon resonance (SPR) strategy and chemiluminescence strategy, have also gained strong driving forces in the detection of pesticide due to their convenient manipulation and high efficiency. By taking advantage of the outstanding distinguish ability provided by recognition unit, SPR and chemiluminescence strategy possessed excellent sensitivity and selectivity for real-time monitoring (see Yan et al. 2018 for details on some of the attractive research on SPR and chemiluminescence strategy).

Outcome and perspectives: Continuous concerns over pesticide residues have provided a long-driven force to develop novel techniques. In the past decade years, thousands of research literatures have been published for the routine and convenient monitoring of pesticide to meet increasing market and social requirements. Yan et al. (2018) have recently reviewed various kinds of optical strategy that were ingeniously designed and successfully applied for the detection of pesticide, with a specific focus on the fluorescence, colorimetric and surface-enhanced Raman scattering sensing strategies. With the emergence of high affinity of recognition elements, as well as various novel signal transduction approaches, optical assay reveal good performance to quantify pesticide residues in complex environment and food matrices, especially in the simplification and visualization design, making them ideally suitable for on-site application.

On the basis of the discussed research, the stability, accuracy, sensitivity and selectivity of optical sensor can be improved as follows: (1) the development of recognition units with excellent distinguish capacity to offer selectivity and sensitivity toward targeted analytes. For example, bi-enzyme cascade catalytic format has the merit of multi-signal amplification, greatly improving the sensitivity. (2) the utilization of novel nanomaterials that employ as signal reporters, substrates and catalysts. Ratiometric probe with dual-emission can provide built-in correction to eliminate environmental effects, exhibiting advantage in terms of enhanced sensitivity and accuracy. Nanozymes possess lower cost, higher stability, and excellent recyclability in comparison with natural enzymes, which improved the stability of sensor. Furthermore, the integration of optical strategy into paper-based analytical devices can be constructed in simplicity and miniaturization, further promoting the commercialization of devices.

Even though optical sensor has a promising future in pesticide determination, there are sustainable challenges to be addressed in the field. Particularly, most optical sensors still retain at laboratory level of testing and verifying proof-of-concept, which have not been exploited in practical applications. In the aspect of recognition events, the stability of recognition units (such as enzymes, antibody and aptamer) can be easily influenced by environmental conditions, such as temperature and pH. Furthermore, the integration of recognition event into the analytical system is a vital step in the fabrication of a successful sensor. The conjugation between recognition elements and functionalised nanomaterials will inevitably increase the complexity, cost and time of optical sensor, especially suppress the distinguish ability of recognition elements. From the perspective of nanomaterials, nanomaterials-based analytical platforms are in the starting stage of development. The specificity and catalytic activity of current nanozymes are lower than that of natural enzymes, in turn impeding the use of nanozymes. The synthesis of functional materials/nanomaterials with relatively narrow size distribution will seriously influence the performance of sensors, because inhomogeneous distribution of nanoprobe can reduce analysis accuracy. Thus, future endeavors should directly focus on addressing above obstacles.

While remarkable progress has been made toward the design of optical sensor for pesticide detection, tremendous opportunities and new trends are emerging. Coupling newly developed recognition elements (nanobodies, peptide aptamers and so on) with functional materials/nanomaterials will afford exciting opportunities for the monitoring of pesticide, which can improve the performance of sensors. On the other hands, the integration of field-deployable devices with optical sensor perform promising on-site applications, with the aid of 3D printing technologies, improving the reproducibility and stability of sensors. By taking advantage of miniaturized device and wire-less networking, the recognition event of pesticide can be transformed into a measurable digital signal by hand-held devices, such as smartphone, then the detection results can deliver to the servers. Thus, the portable detecting platforms can be carried out outside of laboratory setting with minimal user involvement, paving the way for a new generation of analytical devices in real-time detection. Yan et al. (2018) envision that, therefore, optical sensors will assuredly act significant roles in future on-site monitoring of pesticide.

Electrochemical sensors

Electrochemical sensors based on carbon nanotubes: In Table 10.1, the most relevant works related to pesticide electrochemical monitoring using carbon nanotubes-based electrochemical sensors reported in recent years are summarised. From that, Wong et al. (2017) have made a general overview of the current scenario related to this research topic, and, as can be seen, a number of works have been reported using different electrode architectures for the detection of various target analytes. Electrochemical sensors designed with pristine carbon nanotubes or combinations of carbon nanotubes with other modifiers can be found amongst these. There are modified electrodes consisting of CNTs and ionic liquids (ILs), porphyrin, phthalocyanines, metallic nanoparticles, and others. Thus, Wong et al. (2017) discussed the technical issues and the main analytical features, as well as the future challenges of these reports in specific subsections, which were classified according to the type of electrode modifier.

The review after Wong et al. (2017) demonstrated that carbon nanotubes provided electrochemical sensors with relatively good analytical performance in pesticide determination. Pesticides from different classes were electrochemically quantified using carbon nanotubes-based electrochemical sensors. The main electrode modification strategies consisted of the incorporation of carbon nanotubes within the composition of carbon paste electrodes and the modification of the surface of glassy carbon electrodes using the classical dropping cast method. Carbon nanotubes were used alone or in combination with different types of modifiers, including conductive polymers, phthalocyanines, porphyrins, metallic nanoparticles, ionic liquids, and graphene, among others. In general, a typical result achieved from the modification of carbon paste or glassy carbon electrodes is the very high increment of the analytical signal and the displacement of the working potential closer to zero. Both of these effects are desired to ensure high sensitivity and good analytical selectivity. The revised works demonstrated the construction of analytical curves with good linear concentration ranges (typically two concentration decades or more) and low detection limits (at least at the micromolar level). Moreover, in most cases, a good stability of response, precision of measurement, and accuracy in the recovery of spiked environmental samples are proved. Therefore, the positive effects of the use of carbon nanotubes as electrode modifiers for the preparation of electrochemical sensors dedicated to pesticide monitoring is very well illustrated and demonstrated. From the well-established electrochemical sensing performance of carbon nanotubes-based sensors toward pesticides, a set of challenges should be investigated and overcome for the advance of this important research topic.

Table 10.1: Electrochemical sensors based on carbon nanotubes for the detection of pesticides (after Wong et al., 2017)

D3.1 tab10.01

An interesting approach for future investigations is the possibility of designing multiplexed arrays using microfluidic devices, with which different analytes could be simultaneously determined in different sensing points. This challenge is linked with a current and relevant trend in (electro)analytical chemistry, which is the miniaturization of the analytical devices, with minimization of the consumption of chemical reagents and waste generation, as well as the proposition of portable instrumentation for analysis in the field (outside of the lab doors). From an analytical point-of-view, the amperometric and voltammetric methods dedicated to the sensing of pesticides should to be subjected to more rigorous analytical tests in order to verify the selectivity and reproducibility (and improve them if necessary), long-term stability, and applicability in diversified matrice samples, once most of the electroanalytical methods are employed in an analysis of spiked water samples using bulk electrodes. The robustness of the electroanalytical methods must also be evaluated from the analysis of a great number of environmental samples. In terms of sensor architecture material, a current trend is the preparation of composites of carbon nanotubes with another allotropic carbon forms, such as carbon black, graphene, or diamond. These classes of carbon composite electrodes are very promissory for electroanalysis purposes, and future electrochemical investigations should be carried out on the sensing and biosensing of pesticides.

Biosensors

A biosensor is an analytical device, used for the detection of an analyte, combining a biological component (bioreceptor represented by biomolecules or synthetic molecules obtained using biological scaffolds) with a physico-chemical detector, as well as an associated electronic system, which amplifies, process and display the detected signal. A successful biosensor must use a highly specific biocatalyst, stable in various stirring, pH, and temperature conditions (most often enzymes) (Schöning and Poghossian, 2002), give a dose-dependent and, desirably, real-time response, be costeffective, portable, easy to use (Grieshaber et al., 2008).

Biosensors are used in a wide range of applications for the quick and easy detection of pesticides and water contaminants. Gheorghe et al. (2017) present an extensive review of biosensors including:

Electrochemical biosensing techniques used for pesticides detection
Optical and imaging biosensing methods
Immunosensors
Whole-cell based biosensors

Considering the electrochemical biosensing techniques, Ramnani et al. (2016) report that biosensors based on carbon nanostructures are suitable for the design of portable and point-of-use/field –deployable assay kits. Carbon allotropes such as graphene and carbon nanotubes, have indeed been incorporated in electrochemical biosensors for highly sensitive and selective detection of various analytes, due to their many advantages for such applications, like high carrier mobility, ambipolar electric field effect, high surface area, flexibility and compatibility with microfabrication techniques. A simple and sensitive electroanalytical method for cyclic voltammetry and differential pulse voltammetry determination using a magnetic nickel ferrite (NiFe2O4)/MWCNTs nanohybrid-modified GCE has been developed. The method was used to detect benomyl in real samples with satisfactory results (Wang et al., 2015).

Piezoelectric Biosensors, as immunosensors based on acoustic waves, are of emerging interest because of their good sensitivity, real-time monitoring capability, and experimental simplicity (Jia et al., 2012). Piezoelectric systems have emerged as ones of the most attractive biosensing assays for the biopesticides detection due to their simplicity, low instrumentation costs, possibility for real-time and label-free detection and generally high sensitivity. Piezoelectric crystals such as quartz vibrate with characteristic resonant frequency depending on their thickness and cut under the influence of an electric field. The resonant frequency will modify when different molecules adsorb or desorb from the surface of the crystal, and the induced changes are detected by an electronic circuit. Biosensors based on the quartz crystal microbalance have been reported in the literature for organophosphate and carbamate pesticide analysis (Marrazza, 2014).

As a part of developing new systems for continuously monitoring the presence of pesticides in groundwater, a microfluidic amperometric immunosensor was developed for detecting the herbicide residue 2,6-dichlorobenzamide (BAM) in water. A competitive immunosorbent assay served as the sensing mechanism and amperometry was applied for detection. Both the immunoreaction chip (IRC) and detection (D) unit are integrated on a modular microfluidic platform with in-built microflow-injection analysis (μFIA) function. The immunosorbent, immobilized in the channel of the IRC, was found to have high long-term stability and withstand many regeneration cycles, both of which are key requirements for systems utilized in continuous monitoring. Detection of BAM standard solutions was performed in the concentration range 0.0008-62.5 μg/L, which demonstrate the potential of the constructed μFIA immunosensor as an atline monitoring system for controlling the quality of groundwater supply (Uthuppu et al., 2015).

Paper-based sensors

Busa et al. (2016) present a review of paper-based analytical devices (μPADs) that incorporate different detection methods such as colorimetric, electrochemical, fluorescence, chemiluminescence, and electrochemiluminescence techniques for food and water analysis. In Table 10.2., different paper-based platforms are presented.

Table 10.2: Summary of pesticides and insecticides for food and water analyses on paper-based platforms (after Busa et al., 2016)

D3.1 tab10.02

[1] Wang, S.; Ge, L.; Li, L.; Yan, M.; Ge, S.; Yu, J. Molecularly imprinted polymer grafted paper-based multi-disk micro-disk plate for chemiluminescence detection of pesticide. Biosens. Bioelectron. 2013, 50, 262–268.
[2] Sicard, C.; Glen, C.; Aubie, B.; Wallace, D.; Jahanshahi-Anbuhi, S.; Pennings, K.; Daigger, G.T.; Pelton, R.; Brennan, J.D.; Filipe, C.D.M. Tools for water quality monitoring and mapping using paper-based sensors and cell phones. Water Res. 2015, 70, 360–369.
[3] Nouanthavong, S.; Nacapricha, D.; Henry, C.; Sameenoi, Y. Pesticide analysis using nanoceria-coated paper-based devices as a detection platform. Analyst 2016, 141, 1837–1846.
[4] Liu, W.; Kou, J.; Xing, H.; Li, B. Paper-based chromatographic chemiluminescence chip for the detection of dichlorvos in vegetables. Biosens. Bioelectron. 2014, 52, 76–81.
[5] Liu, W.; Guo, Y.; Luo, J.; Kou, J.; Zheng, H.; Li, B.; Zhang, Z. A molecularly imprinted polymer based a lab-on-paper chemiluminescence device for the detection of dichlorvos. Spectrochim. Acta. A Mol. Biomol. Spectrosc. 2015, 141, 51–57.
[6] Badawy, M.E.I.; El-Aswad, A.F. Bioactive paper sensor based on the acetylcholinesterase for the rapid detection of organophosphate and carbamate pesticides. Int. J. Anal. Chem. 2014, 2014, 536823.
[7] Sun, G.; Wang, P.; Ge, S.; Ge, L.; Yu, J.; Yan, M. Photoelectrochemical sensor for pentachlorophenol on microfluidic paper-based analytical device based on the molecular imprinting technique. Biosens. Bioelectron. 2014, 56, 97–103
[8] Su, Y.; Ma, S.; Jiang, K.; Han, X. CdTe-paper-based Visual Sensor for Detecting Methyl Viologen. Chin. J. Chem. 2015, 33, 446–450.

With the goal to devise portable and easy measuring techniques and considering the increasing use of smartphones, the number of μPAD strategies that incorporate mobile or smartphones for target measurements is increasing. For instance, Sincard et al. (2015) describe a combination of paper-based sensors as an ultra-low cost approach for large-scale monitoring of water quality. The paper-based analytical device (mPAD) produces a colorimetric signal that is dependent on the concentration of a specific target, including organophosphate pesticides in water. A mobile phone equipped with a camera for capturing images of two mPADs e one tested with a water sample and the other tested with clean water that is used as a control, and an on-site image processing app that uses a novel algorithm for quantifying color intensity and relating this to contaminant concentration (Figure 10.1). The mobile phone app utilizes a pixel counting algorithm that performs with less bias and user subjectivity than the typically used lab-based software, ImageJ. The use of a test and control strip reduces bias from variations in ambient lighting, making it possible to acquire and process images on-site. The cell phone is also able to GPS tag the location of the test, and transmit results to a newly developed website, WaterMap.ca™, that displays the quantitative results from the water samples on a map. We demonstrate our approach using a previously developed mPAD that detects the presence of organophosphate pesticides based on the inhibition of immobilized acetylcholinesterase by these contaminants. The objective of this paper is to highlight the importance and potential of developing and integrated monitoring system consisting of mPADs, cell-phones and a centralised web portal for low-cost monitoring environmental contaminants at a large-scale.

D3.1 fig10.01
Figure 10.1

2. Sensors for nitrate measurement in water

In their upcoming review on spectroscopic methods for determination of nitrite and nitrate in environmental samples, Singh et al. (2019) extensively described the different laboratory methods referring 229 publications on the topic.

According to Azmi et al. (2017), many researchers in the field of potentiometry, electrochemical, and biosensors have focused on miniaturising their detection systems to enhance the capability of nitrate in-situ measurement. The performance of miniaturised sensor systems is comparable to that of conventional systems.

Potentiometry sensors

Basically, the conventional architecture of the system consists of two electrodes known as the working electrode and the reference electrode; a salt bridge, and a voltmeter. Figure 10.2(a) illustrates the architecture of the conventional potentiometry system. Meanwhile Figure 10.2(b) illustrates that of the miniaturised potentiometry system.

The advantages of this technique are its low cost (Hassan et al., 2007, Zhang et al., 2015, Mendoza et al., 2014, Paczosa-bator et al., 2014), non-destruction of sample, portable device (Zhang et al., 2015, Mendoza et al., 2014, Chang et al., 2013, Hassan et al., 2007, Santos et al., 2004) with fast response/feedback (Zhang et al., 2015, Li and Li, 2010, Paczosa-bator et al., 2014, Chang et al., 2013, Santos et al., 2004) and the requirement of minimum sample pretreatment.

Research of the potentiometry system has followed several avenues. Early work by Hassan (1976) was concerned with organic nitrate ions and nitramine determination based on the reaction with mercury sulphuric acid mixture. Mendoza et. al. (2014) characterised a nanobiocomposite as Ion Selective Electrodes (ISE) for nitrate ion determination in water. Mahajan et. al. (2007) developed a polymeric membrane by means of Zn (||) complex-based electrodes that work as anion carriers for nitrate anion determination in water. Li and Li (2010) and Nuñez et al. (2013) predict the nitrate contamination level in water based on an artificial neural network (ANN) algorithm.

D3.1 fig10.02
Figure 10.2 D31 tab1003
Table 10.3

Azmi et al. (2017) remind that the use of a membrane helps the potentiometry system to be selective to nitrate ions and is one of the factors that affects the system’s limit of detection (LOD). Bendikov and Harmon (2005) mentioned that doped polypyrrole (PPy(NO₃^-)) is a highly selective membrane in an ISE system for nitrate determination in water. They revealed that conductive polymer polypyrrole is widely used due to its high conductivity ability and it being relatively stable. As a result, Zhang et al. (2015) took the initiative to apply doped polypyrrole as a sensitive membrane material for the potentiometry system. The polypyrrole could improve selectivity, simplify the recipe procedure, and reduce toxicity compared to the conventional non-porous polyvincyl chloride (PVC) ISE (Zhang et al., 2015). Moreover, this study successfully demonstrated that the use of carbon nanostructure materials between the membrane and the substrate layer in the electrode structure of potentiometric system could prevent the water formation that led to instability. Meanwhile, Mahajan et. al. (2007) developed a polymeric membrane that was made of zinc (||) complex for selective nitrate determination in water. The finding demonstrates that the output of a potentiometry system using zinc (||) complex membrane exhibits better selectivity for nitrate ions than for other inorganic anions. They highlighted the advantages of zinc (||) complexes, such as stable detection reproducibility and being highly sensitive to nitrate. Wardak (1976) developed an active membrane component using trihexyltetradecylphosphonium chloride (THTDPCl) for polymeric membrane. THTDPCl could enhance the PVC membrane sensitivity by reducing electrical resistance.

The majority of potentiometric nitrate sensors that integrated either true-liquid or liquid polymeric membranes are bulky due to the tubular design with internal reference electrode and internal reference electrolyte solutions. Thus, a micro-fabricated planar potentiometric sensor was introduced (Hassan et al., 2007, Calvo-lópez et al., 2013). The micro-scale sensor could provide several advantages such as small size, simple design, low cost and mass production. Various materials are introduced to produce a micro-scale potentiometric sensor chip. Such materials are screen-printed thick film, silicon transducer chip, silicon nitride base chip and metal printed flexible polyimide film. Current miniaturised micro scale sensors for nitrate detection demonstrate a good response towards nitrate ions.

The miniaturisation of ISEs, while maintaining their selectivity and sensitivity, is a crucial step in the next phase of ISE evolution. Traditionally, in so-called coated-wire ISEs, the ion-selective membrane is placed directly on a solid electronically conductive support, thereby removing the need for an inner solution. However, in these devices, it was observed that the long-term potential stability was quite limited, and they were useful only in specific applications such as capillary electrophoresis or in flow-injection analysis. An important breakthrough in ISE design was achieved by the application of conducting polymers (CPs) as a solid contact layer, i.e. a mediating layer between the electronically conducting substrate and ionically conducting ISE membrane, which was possible due to the mixed conductivity of CPs. Various conductive polymers have been examined as possible internal contact materials that could simultaneously stabilise the overall electrode potential and remove the need for an inner filling solution.

Basically, the conventional architecture of the system consists of two electrodes known as the working electrode and the reference electrode, a salt bridge, and a voltmeter.