Pesticide Contamination Of Groundwater Research Articles

Integrated management of pesticides in an intensive agricultural area: a case study in Altinova, Turkey

Pesticide contamination of groundwater is a common critical problem faced by many countries due to excessive and unconscious applications. As a result of increasing concerns about pesticides, several qualitative and quantitative risk assessment models/indicators were developed and applied. In this study, a practical approach was presented for the protection of groundwater from pesticide contamination. The first phase is the assessment of the specific vulnerability of groundwater to pesticide contamination using the DRASTIC-Pesticide model. The second phase is the monitoring and assessment of groundwater quality to verify vulnerability assessment. The third phase is to assess the impacts of pesticides on the environment and human health using a commonly applied pesticide risk indicator, the environmental impact quotient (EIQ). The pilot study area (PSA) is the Altinova region at Antalya city of Turkey which exhibits intensive agricultural activities and covers an approximate surface area of 75 km2. A total of 25 groundwater wells were chosen for monitoring of groundwater quality where four sessions of seasonal field measurements were conducted for 1 year. Two sessions of water quality analyses were also performed for many physical, bacteriological, and chemical parameters, including pesticides. Additionally, soil samples were analyzed, site surveys were conducted, and other relevant information (topographical, geological and meteorological characteristics, pesticide use and toxicological data sets, etc.) was gathered. The PSA was determined to have high vulnerability to contamination of groundwater, and it was verified through monitoring results. The commonly used pesticides in the PSA were ranked according to their risks to select pesticides with the least environmental impacts.

Four-year advanced monitoring program of polar pesticides in groundwater of Catalonia (NE-Spain)

Pesticide contamination of groundwater is of paramount importance because it is the most sensitive and the largest body of freshwater in the European Union. In this paper, an isotopic dilution method based on on-line solid phase extraction–liquid chromatography (electrospray)–tandem mass spectrometry (SPE–LC(ESI)–MS/MS) was used for the analysis of 22 pesticides in groundwater. Results were evaluated from monitoring 112 wells and piezometers coming from 29 different aquifers located in 18 ground water bodies (GWBs), from Catalonia, Spain, for 4years as part of the surveillance and operational monitoring programs conducted by the Catalan Water Agency. The analytical method developed allows the determination of the target pesticides (6 triazines, 4 phenylureas, 4 organophosphorous, 1 anilide, 2 chloroacetanilides, 1 thiocarbamate, and 4 acid herbicides) in groundwater with good sensitivity (limits of detection <5ng/L), accuracy (relative recoveries between 85 and 116%, except for molinate), and repeatability (RSD<23%), and in a fully automated way. The most ubiquitous compounds were simazine, atrazine, desethylatrazine and diuron. Direct relation between frequency of detection of each target compound and Groundwater Ubiquity Score index (GUS index) is observed. Desethylatrazine and deisopropylatrazine, metabolites of atrazine and simazine, respectively, presented the highest mean concentrations. Compounds detected in less than 5% of the samples were cyanazine, molinate, fenitrothion and mecoprop. According to the Directive 2006/118/EC, 13 pesticides have individual values above the requested limits (desethylatrazine, atrazine and terbuthylazine lead the list) and 14 samples have total pesticide levels above 500ng/L. The GWB with the highest levels of total pesticides is located in Lleida (NE-Spain), with 9 samples showing total pesticide levels above 500ng/L. Several factors such as regulation of the use of pesticides, type of activities in the area, and irrigation were discussed in relation to the observed levels of pesticides.

Evaluation of groundwater contamination in a coastal area of south-eastern Sicily

This investigation was under taken to evaluate the groundwater resources contamination due to intensive agricultural practices (particularly greenhouses). The study-area is located in the coastal area of the Ragusa province (South-East Sicily), where numerous existing greenhouses may cause the contamination of groundwater systems (unconfined and confined aquifers) beneath the cropped land. The pollution risk is mainly related with the seepage process of macro-elements nitrogen (N), phosphorus (P), potassium (K), held in the irrigation water and the massive use of fertilizers and pesticides, that may pass through the unsaturated zone of the soil profile. Moreover, the area is characterized by the presence of several wells (about 15 wells/km2) for agricultural use that cause the aquifer overexploitation and the consequent risk of seawater intrusion. The agriculture practices adopted in the study area (irrigation volumes, fertilizer concentrations, use of pesticides…) were monitored since February 2009; moreover, the pollution risk of the aquifers was evaluated through the analysis of groundwater water samples collected (monthly) in the monitoring wells; in particular, nitrogen compounds, soluble phosphorous (PO4 −−), potassium, as well as the main pesticides commonly used in the study area, were measured.The results show that electrical conductivity and chloride concentration values can cause reduction of production and leaf damage problems, respectively, for most of the monitored farm systems. The high nitrogen compounds concentrations observed in the monitored wells can cause health and environmental problems. Moreover high pesticide contamination of groundwater was found in two of the five monitored wells.

Fifth national survey of pesticides in groundwater in New Zealand

A total of 163 wells were sampled in New Zealand as part of the 2006 national survey of pesticides in groundwater. The aims of the survey were to update the national overview of pesticides in New Zealand's groundwater systems, to investigate temporal variation in pesticide concentrations between surveys, and to identify environmental factors associated with pesticide contamination of groundwater. Thirty‐one wells (19%) tested positive for pesticides, with 13 (8%) wells having two or more pesticides detected. Pesticides were measured in one or more wells in 11 out of the 14 regions sampled; they were not detected in wells from the Northland, Hawke's Bay, and Taranaki regions. Nineteen different pesticides and metabolites were detected in groundwater. Herbicides were the most common pesticide group detected (12), followed by insecticides (5) and fungicides (2). There was a total of 50 pesticide detections and, of these, 37 were herbicides and 25 were triazine herbicides. Levels of only two of the 50 pesticide detections exceeded 1 μg litre‐1. Alachlor was detected in one well at a concentration of 34 μg litre‐1 exceeding the maximum acceptable value (MAV) of 20 μg litre‐1. All other pesticides were detected at concentrations less than 6% of the MAV. There were significant differences between shallow and deep wells with shallow wells being associated with pesticide detections. Higher dissolved oxygen and nitrate concentrations (indicating recent water), lower groundwater pH levels, urban and horticultural land use and unconfined aquifers were associated with pesticide detections. Comparisons of total pesticide concentrations in wells included in the previous surveys indicate that total target pesticide concentrations in groundwater are decreasing.

Toward a Better Understanding of Contamination of Ground Water by Pesticides

Public awareness of pesticides in ground water has been heightened by numerous reports in newspapers, in magazines, and on television. Yet, the understanding of processes causing contamination of ground water by pesticides remains insufficient. Indeed, the literature on pesticide fate and transport decreases exponentially with increasing depth below the soil surface. Considering the entire continuum of the unsaturated zone (not only the soil but also the whole depth below the root zone) and the saturated zone, the transport and fate of not a single pesticide has been accurately simulated, not even within an order of magnitude of the concentration observed. The problem is exacerbated by the quasi-systematic presence of several substances in any given sample. What pesticide must we look for, where, and when? Will the present contamination increase or decrease? What is the economic cost of the contamination? None of these questions has a unique, straightforward answer widely accepted by the scientific community. This situation is unacceptable not only for earth scientists but also primarily for water managers who are charged with setting up policies to reduce existing contamination and prevent future occurrences. Hundreds of pesticides are registered worldwide, and metabolites are often found with a greater frequency and higher concentration than the parent compound. Current procedures to assess the potential of a pesticide to leach to ground water are not sufficient to decide which pesticides should be monitored in each specific situation. Indeed, the data bases on pesticide loads at the soil surface derive from agricultural statistics or manufacturer or distributor inquiries at the regional (or national) scale and do not correspond to the spatial boundaries of the aquifers or local agricultural practices. Furthermore, these data bases do not enable the location of the applications at plot scale, even though such a precise location is needed to link observed concentrations in a well to loading at the soil surface. We urgently need appropriate data bases at the aquifer scale to identify the suite of substances to be analyzed and to quantify pesticide input functions. In parallel, monitoring networks must be developed and operated over long time frames in view of the slow time response of many aquifers. Preferential transport of pesticides through the soil has been a hot topic over the past decade, but its actual influence on observed ground water concentrations has not been adequately demonstrated. Depending on the hydrodynamics in the unsaturated zone below the root zone and in the saturated zone, concentration peaks from preferential transport in the soil zone may be smeared or remain unaltered in the saturated zone. Dedicated field studies that focus on the structure, hydrodynamic, and biogeochemical properties of the subsurface are needed. Additionally, models are needed that dynamically link unsaturated and saturated zone processes to represent the effect of preferential transport of pesticides in the soil on ground water contamination. More information is required on the adsorption and (bio)degradation properties of a range of pesticides (and their metabolites) along with the solids in the subsurface with which they are in contact. Great care is needed to conduct these studies under (sub)-μg/L concentrations and incubation times up to years. The potential for adaptation of microorganisms to degradation of pesticides must also be considered. The mass of pesticides present in the unsaturated zone and its availability for mobilization by recharge water also remain largely unknown. Analytic chemists must reach quantification limits less than 0.1 μg/kg for pesticides in water saturated and unsaturated solids, and sampling procedures appropriate for such pesticide determinations must be developed. We also lack data on the economic cost of pesticide contamination of ground water. Neither the total damage costs nor the potential benefits of alternative management practices have been adequately assessed at regional or national scales. The assessment of effectiveness is absolutely required to verify the potential benefits of mitigation policies, which are sometimes described as disproportionately costly by farmers and agrochemical lobbies. Field studies at the aquifer scale are needed and the obstacles to such studies, not all of which are simply financial, must be overcome at least for a selection of sites. Otherwise, we will continue to understand little about pesticides in ground water for quite awhile.

Source and persistence of pesticides in a semi-confined chalk aquifer of southeast England

Pesticide contamination in groundwater is an increasing problem that poses a significant long-term threat to water quality. Following the detection of elevated concentrations of diuron in boreholes in a semi-confined chalk aquifer from southeast England, a sampling programme was undertaken. Between 2003 and 2004 diuron was observed in 90% of groundwaters analysed. In 60% of groundwater samples metabolites of diuron were more prevalent than the parent compound. Longer-term (1989–2005) monitoring shows that pollution of the aquifer by atrazine, simazine, and more recently diuron, shows a positive correlation with periods of high groundwater levels. Results from groundwater residence time indicators suggest that the highest diuron concentrations are associated with waters containing the greatest proportion of recent recharge. There is some evidence to indicate that diuron occurrence can be spatially related to areas of urban and industrial development and is probably correlated with amenity usage.

Organochlorine pesticide contamination of ground water in the city of Hyderabad

Organochlorine pesticides are ubiquitous and persistent organic pollutants used widely throughout the world. Due to the extensive use in agriculture, organic environmental contaminants such as HCH, DDT along with other organochlorine pesticides are distributed globally by transport through air and water. The main aim of present study is to determine contamination levels of organochlorine pesticides in the ground water of Hyderabad City. Water samples were collected from 28 domestic well supplies of the city. For this study, random sampling technique was applied, all the samples were collected in high purity glass bottles and refrigerated at 4 °C until analysis. Solid Phase Extraction (SPE) is used for the extraction of organochlorine pesticide residues in water sample. The collected water samples were pre-filtered through a 0.45 μg glass fiber filter (Wattman GF/F) to remove particulate matter and were acidified with hydrochloric acid (6N) to pH 2.5. Methanol modifier (BDH, for pesticide residue analysis, 10 mL) was added to water sample for better extraction. SPE using pre-packed reversed phase octadecyl (C-18 bonded silica) contained in cartridges was used for sample preparation. Prior to the extraction, the C-18 bonded phase, which contains 500 mg of bonded phase, was washed with 20 mL methanol. The sample was mixed well and allowed to percolate through the cartridges with flow rate of 10–15 mL/min under vacuum. After sample extraction, suction continued for 15 min to dry the packing material and pesticides trapped in the C-18 bonded phases were eluted by passing 10 mL hexane and fraction was evaporated in a gentle steam of Nitrogen. In all samples pesticide residues were analyzed by GC (Chemito-8510) with Ni63 ECD detector. Helium was used as carrier gas and nitrogen was used as make up gas. The injection technique was split/split less. All the samples analyzed were found to be contaminated with four pesticides i.e. DDT, β-Endosulfan, α-Endosulfan and Lindane. DDT was found to range between 0.15 and 0.19 μg L−1, β-Endosulfan ranges between 0.21 and 0.87 μg L−1, α-Endosulfan ranges between 1.34 and 2.14 μg L−1 and Lindane ranges between 0.68 and 1.38 μg L−1 respectively. These concentrations of pesticides in the water samples were found to be above their respective Acceptable Daily Intake (ADI) values for Humans.

Nitrate and pesticide contamination of groundwater under rice-based cropping systems: past and current evidence from the Philippines

The quality of shallow groundwater used for domestic purposes by the rural poor in developing countries is threatened by contamination with nitrate and residues of pesticides used in agriculture. In Asia, many of the rural poor live in rice-producing areas where the continuous flooding of rice ( Oryza sativa) fields may lead to high leaching rates of groundwater contaminants. This study presents results of measurements of nitrate and pesticide concentrations in shallow groundwater in 54 domestic wells under rice-based production systems in Luzon, Philippines, from 1989 to 2000. In irrigated double rice cropping areas, seasonal-mean nitrate concentrations were 0–2 mg l −1, which is below the WHO limit of 10 mg l −1 for drinking water. In wet season (WS) rainfed rice and dry season (DS) irrigated sweet pepper ( Capsicum annuum) double cropping areas, monthly mean nitrate concentrations were 5–12 mg l −1. Nitrate concentrations were lower under other, less fertilized upland crops, and with a high percentage of the area under rice in the WS. Mean pesticide concentrations were generally one to two orders of magnitude below the WHO single (0.1 μg l −1) and multiple pesticide (0.5 μg l −1) limits, although temporary peak concentrations of 1.14–4.17 μg l −1 were measured. For both nitrate and pesticides, the high leaching potential appears to be offset by the particular transformation and loss processes taking place under tropical, anaerobic conditions. The agro-ecological environment and history of the study sites suggest that the results may be characteristic of many parts of tropical Asia where rice-based cropping has intensified since the Green Revolution in the mid-1960s.

Evaluation of Pesticide Contamination of Ground Water in Two Agricultural Areas of Portugal

In two Portuguese agricultural areas, "Beira Litoral" and "Ribatejo e Oeste", several pesticides regularly applied in vineyards, maize, potato, tomato for industry, apple, pear and rice were detected in ground water. Atrazine was the most frequently detected, being found in 70% of the total of 79 sites selected in the year 2000, followed by its metabolites desethylatrazine and desisopropylatrazine with frequencies of detection, respectively, of 56% and 48% and by simazine (37%), alachlor (25%), metolachlor (24%) and metribuzin (15%). Other pesticides and metabolites i.e. 3,4-dichloroaniline, dimethoate, f and g -endosulfan, lindane, molinate and prometryn were also detected but at lower occurrences. Pesticides were detected mainly in ground water wells used for irrigation purposes, although in some locations they were also found in water wells used for human consumption. In this study, it was also observed a seasonal variation of pesticide residues in ground water of shallow and deep wells.

Biotransformation of pesticides in saturated-zone materials

Many studies have been conducted to evaluate pesticide contamination of groundwater in the United States, but investigations of pesticide biotransformation in saturated zones are much less numerous than in surface soils. Because results of studies using soils are not directly applicable to the subsurface, the purpose of this paper is to illustrate examples of pesticide biotransformation in saturated-zone materials. Although it must be considered with caution, the US Environmental Protection Agency's (EPA) "Pesticides in Ground Water Database" was used to focus the discussion on the biotransformation potential of dibromoethane (EDB), atrazine, acetanilide herbicides, and aldicarb, all of which have been detected in groundwater in the United States. Results of more than two dozen studies indicate that a biotransformation potential for these pesticides exists in saturated-zone materials, although for any given pesticide substantial differences in biotransformation occurred. These variations were due both to differences in experimental methods and to heterogeneities in the subsurface materials under investigation. However, because biotransformation mechanisms were not well investigated, it is generally not possible to extrapolate predictions of biotransformation potential beyond the specific sites investigated. These results highlight the need to better understand microbial genetic regulation of biotransformation processes so that genetic information may be effectively incorporated into future investigations of biotransformation potential in the subsurface.

Factors affecting atrazine fate in north central U.S. soils.

Atrazine persistence and fate are influenced by many factors, the interactions of which are difficult to predict. Several models, such as LEACHP (Wagenet and Hutson 1989), have been used as tools to estimate losses and identify variables that will impact the magnitude of loss. The LEACHP model was evaluated for predicting atrazine movement in sandy loam, silt loam, and clay loam soils during three consecutive years (two dry and one wet) in Minnesota (Khakural et al. 1995). Considering the broad range in soil properties and climatic conditions used in testing, the model performed well. However, these are only estimates, and additional field studies need to be conducted to verify model results. In a report by Fausey et al. (1995), the amount of atrazine found in groundwater throughout the Midwestern region was reported to be much below the MCL. However, specific sites in the Midwest may struggle with atrazine problems from both point and nonpoint sources of contamination. Some states, such as South Dakota, have created groundwater protection areas that alert growers and the public to sensitive areas where contamination may occur because of soil type, depth to groundwater, and distance to public wellheads. Wisconsin has developed a tiered managerial strategy, or zoning approach, in which restrictions are matched to pollution detections (Wolf and Nowak 1996). The USEPA has mandates for states to implement generic management plans to prevent pesticide contamination of groundwater. Chemical-specific plans by states will be required for at least five pesticides, one of which will be atrazine. Best management practices have been and are continuing to be developed to aid the grower in lessening the adverse impacts of atrazine. With continuing research into understanding the problem and developing solutions, and with adaptation of these recommendations by growers, the use of effective, inexpensive herbicides may continue with minimal off-site environmental effects.

An analytical model for the assessment of pesticide exposure levels in soils and groundwater

The movement and degradation of pesticide residues in soils and groundwater are complex processes affected by soil physical, (bio)chemical, and hydrogeological properties, climatic conditions, and agricultural practices. This work presents a physically-based analytical model suitable for long-term predictions of pesticide concentrations in groundwater. The primary interest is to investigate the impact of soil environment, related physical and (bio)chemical processes, especially, volatilization, crop uptake, and agricultural practices on long-term vulnerability of groundwater to contamination by pesticides. The soil is separated into root and intermediate vadose zones, each with uniform properties. Transport in each soil zone is modeled on the basis of complete mixing, by spatial averaging the related point multiphase-transport partial differential equation (i.e., linear-reservoir models). Transport in the aquifer, however, is modeled by a two-dimensional advection-dispersion transport equation, considering adsorption and first-order decay rate. Vaporization in the soil is accounted for by assuming liquid-vapor phase partitioning using Henry's law, and vapor flux (volatilization) from the soil surface is modeled by diffusion through an air boundary layer. Sorption of liquid-phase solutes by crops is described by a linear relationship which is valid for first-order (passive) crop uptake. The model is applied to five pesticides (atrazine, bromacil, chlordane, heptachlor, and lindane), and the potential for pesticide contamination of groundwater is investigated for sandy and clayey soils. Simulation results show that groundwater contamination can be substantially reduced for clayey soil environments, where bio(chemical) degradation and volatilization are most efficient as natural loss pathways for the pesticides. Also, uptake by cross can be a significant mechanism for attenuating exposure levels in ground-water especially in a sandy soil environment, and for relatively persisting pesticides. Further, simulations indicate that changing agricultural practices can have a profound effect on vulnerability of groundwater to mobile and relatively persisting pesticides.

Pesticide Contamination in Groundwater on Okinoerabu Island, an Intensive Agricultural District in Japan.

沖永良部島は日本の南西諸島における典型的な農業地域の一つである. 同島の北東半分を占める和泊町においては, 花き栽培などの集約的農業のために土地面積当たりの農薬消費量が日本全国の平均の3倍以上に達している. 同島において, 33地点の115の地下水サンプルの中の混入農薬(フェニトロチオン, ダイアジノン, プロチオホス, キャプタン)を分析した. 8地点の15サンプルからこれら4種の農薬のうちいずれかが検出された. この結果は, 日本においてもゴルフ場ばかりでなく集約的な農業のために施用される農業によって地下水が汚染される場合があることを示している. キャプタンは, 分析した農薬の中でも最も消費量が多いものであったが, 2サンプルからのみ検出された. これら2サンプルは, 集約的な花き栽培がより盛んな同町北東部からのものであった. フェニトロチオンとダイアジノンは年間を通じて様々な地点から検出された. さらに, 同町におけるこれら2種の農薬の消費量は異なる季節変動を示すにもかかわらず, 最も汚染されていた地点の一つについて, これら2種の農薬の検出濃度の比は毎回ほぼ一定であった. このことから, これらの農業は同島の地下水に比較的緩慢かつ継続的に浸透していくことが示唆される.

An Expert Systems Approach for Assessing the Potential for Pesticide Contamination of Ground Water

AbstractThe EXPRES expert system (EX pert system for Pesticide/Regulatory Evaluations and Simulations) has been developed to assist those who are knowledgeable, but not proficient, in the theory of pesticide transport in the subsurface or in the use of pesticide assessment models with a means of assessing the potential for pesticides to contaminate ground water. EXPRES is not intended to replace expert opinion but rather EXPRES is intended to be used as a screening tool by nonexperts who need to evaluate the potential for pesticides to contaminate ground water. EXPRES combines a knowledge‐based system, a graphically based user‐system interface, extensive geographical and pesticide data bases, and three existing pesticide assessment models (LP/LI, PRZM, and LEACHM). Based on the user's available data, objectives of the assessment and time constraints, EXPRES selects the most appropriate model, assists the user in the construction of an input data set, initiates an assessment, and aids in the interpretation of the results of an assessment model. Specific assistance in the construction of the input data set includes providing pertinent data for characterizing a site or a pesticide from its data bases, assisting the user to respond to a prompt from EXPRES, aiding the user in estimating missing values for pesticide or site parameters, and ensuring the zintegrity of the input data set. The inclusion of three models allows EXPRES to select the model which is most applicable for the objectives on the investigation, including: (1) a review of pesticide properties and site characteristics that influence the fate of pesticides in the subsurface, (2) a relative assessment, with respect to other pesticides, of the potential for a pesticide to leach to the water table, (3) a quantitative prediction of the distribution and migration rates of the pesticide with both time and depth, and (4) an evaluation of the processes and factors controlling the fate of the pesticides in the subsurface.

Pesticide Contamination of Groundwater in Virginia: BMP Impact Assessment

The Nomini Creek Watershed/Water Quality monitoring project was initiated in 1985, as part of the Chesapeake Bay Agreement of 1983, to quantify the impacts of agricultural best management practices (BMPs) on improving water quality. The watershed monitoring system was designed to provide a comprehensive assessment of the quality of surface and groundwater as influenced by changes in land use, agronomic, and cultural practices in the watershed over the duration of the project. The primary chemical characteristics monitored include both soluble and sediment-bound nutrients and pesticides in surface and groundwater. Water samples from 8 monitoring wells located in agricultural areas in the watershed were analyzed for 22 pesticides. A total of 20 pesticides have been detected in water samples collected. Atrazine is the most frequently detected pesticide. Detected concentrations of atrazine ranged from 0.03 - 25.56 ppb and occurred in about 26 percent of the samples. Other pesticides were detected at frequencies ranging from 1.6 to 14.2 percent of all samples collected and concentrations between 0.01 and 41.89 ppb. The observed concentrations and spatial distributions of pesticide contamination of groundwater are compared to land use and cropping patterns. Results indicate that BMPs are quite effective in reducing pesticide concentrations in groundwater.

Pesticide contamination of ground water in the United States - A review

Over 70 pesticides have been detected in ground water. Aldicarb and atrazine along with the soil fumigants EDB and DCP and DBCP have been the pesticides most frequently detected in ground water. Atrazine concentrations have been correlated with high nitrate concentrations. The triazine herbicides, simazine and cyanazine, have also been detected in ground water. The annual amount of recharge, soil type, depth of aquifer from the surface, nitrate contamination and soil pH are important field parameters in determining ground-water contamination potential by pesticides. Pesticide leaching is reduced by proper choice of crop rotation, increasing pesticide application efficiency, and integrated pest management.

Pesticide Contamination of Ground Water Artificially Recharged by Farmland Runoff

AbstractAtrazine, cyanazine, alachlor, and metolachlor in the surface water of a recharge structure, which impounds runoff from row‐cropped farmland in Nebraska, are transported with seepage to the shallow ground water flow system and to the locally confined regional aquifer. All wells in the shallow flow system and all those in the regional flow system impacted by seepage from the structure had detectable concentrations of at least one of the four pesticides.The detectable concentrations of cyanzine, alachlor, and metolachlor in the two flow systems ranged from 0.1 to 0.9 ppb. These concentrations were an order of magnitude lower than those in the surface water. Concentrations in the regional aquifer clustered at the lower end of this concentration range. These three pesticides were not detected in the baseline study of the regional aquifer.Unlike alachlor, cyanzine, and metolachlor, atrazine was always present in the wells impacted by seepage from the recharge structure. In the shallow flow system, concentrations ranged from 0.3 to 8.8 ppb and from 0.1 to 2.5 ppb in the regional aquifer. The average of the detectable atrazine concentrations in the baseline study was 0.04 ± 0.05 ppb.

Pesticide contamination of groundwater in western Europe

In recent years, many measurements have been made of residues of pesticides in shallow and deep groundwater in western Europe. Some triazine herbicides and their transformation products have been detected most frequently. The average concentration in measuring series for deep groundwater was usually below 0.1 μg l −1, and the highest values were usually below 0.5 μg l −1. The concentrations of mecoprop in deep groundwater ranged up to 0.6 μg l −1 and those of bentazone to almost 1.0 μg l −1. Some other herbicides were found at comparatively high concentrations and the highest values were found for TBA and TCA in tile-drain water. The soil fumigant 1,3-dichloropropene was mainly found in shallow groundwater, but its admixture 1,2-dichloropropane was also found in deep groundwater (range up to 10 μg l −1, sometimes even higher). Residues of the nematicides aldicarb and oxamyl have been measured in shallow and intermediate groundwater, but measurements for deep groundwater are still lacking. Some carbamoyl-oximes were incubated in subsoil materials to study their transformation and their rate of transformation in anaerobic subsoils was surprisingly high. The maximum admissible concentration of 0.1 μg l −1 in a Directive of the European Communities of 1980 is the subject of much debate, because a toxicological basis is lacking.