Agricultural Chemicals In Ground Water Research Articles

Variables that Affect Agricultural Chemicals in Groundwater in Nebraska

Agricultural chemicals from nonpoint sources in groundwater are present in the major provinces of the High Plains aquifer in Nebraska. Nitrate and triazine-herbicide concentrations in groundwater were assessed to establish preliminary relations between these constituents and selected hydrogeologic, climatic, and land-use variables. Also, macropore flow paths were measured in an attempt to delineate their contribution to non-point source pollution from the study areas. Water from 82 wells in six study areas was analyzed for nitrate; water from 57 of the 82 wells was analyzed for triazine herbicides. Twenty-one independent variables were identified that could potentially affect chemical concentrations in groundwater. Data for 9 of 21 independent variables suspected of affecting concentrations of nitrate and triazine herbicides in groundwater were collected from the well sites. The nine variables and their measured ranges were hydraulic gradient, 0.0006–0.0053; hydraulic conductivity, 1.5–45.4 m (5–149 ft) per day; specific discharge, 0.004–0.091 m (0.0128–0.2998 ft) per day; depth to water, 0.91–76 m (3–250 ft); well depth, 12–168 m (40–550 ft); annual precipitation, 30–100 cm (12.0–39.3 in.); soil permeability, 1.9–23 cm (0.76–9.0 in.); irrigation-well density, 0–8 irrigation wells per 2.59 km2 (1 square mile); and annual nitrogen fertilizer use, 0–118 kg (0–260 lb) of nitrogen per acre. Macropore flow is listed in percent, average per study area based on determinations from dye studies. In this instance, macropore flow is used to also entail preferential flow paths. Nitrate concentrations ranged from 0.1 to 45 mgL−1. Triazine-herbicide concentrations were detected in samples from five of the six study areas in concentrations ranging from 0.1 to 2.3 μL−1. Analysis indicated that there were significant differences in nitrate concentrations (averages—at 95 % confidence level using Kendall Test) among the six study areas; no significant differences in triazine-herbicide concentrations were found. Concentrations of nitrate and triazine herbicide were determined (using contingency-table analysis), to be significantly larger in more intensively irrigated areas compared to less intensively irrigated areas. Preliminary correlations with the independent variables and nitrate concentrations indicated significant relations at the 95 % confidence level with variables hydraulic conductivity, well depth, and irrigation well density. Correlations with triazine-herbicide concentrations indicated significant relations with hydraulic conductivity, specific discharge, well depth, annual precipitation, and irrigation well density, as well as nitrate concentrations. Simple multiple-regression technique indicated that well depth and density and fertilizer use explained about 51 % of the variation in nitrate concentrations. Specific discharge and well depth explained about 60 % of the variation in triazine-herbicide concentrations. Macropore flow paths and specific discharge explained 84 % of the total variation in triazine-herbicide concentrations. The use of trade names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.

Temporal trends in concentrations of DBCP and nitrate in groundwater in the eastern San Joaquin Valley, California, USA

Temporal monitoring of the pesticide 1,2-dibromo-3-chloropropane (DBCP) and nitrate and indicators of mean groundwater age were used to evaluate the transport and fate of agricultural chemicals in groundwater and to predict the long-term effects in the regional aquifer system in the eastern San Joaquin Valley, California. Twenty monitoring wells were installed on a transect along an approximate groundwater flow path. Concentrations of DBCP and nitrate in the wells were compared to concentrations in regional areal monitoring networks. DBCP persists at concentrations above the US Environmental Protection Agency’s maximum contaminant level (MCL) at depths of nearly 40 m below the water table, more than 25 years after it was banned. Nitrate concentrations above the MCL reached depths of more than 20 m below the water table. Because of the intensive pumping and irrigation recharge, vertical flow paths are dominant. High concentrations (above MCLs) in the shallow part of the regional aquifer system will likely move deeper in the system, affecting both domestic and public-supply wells. The large fraction of old water (unaffected by agricultural chemicals) in deep monitoring wells suggests that it could take decades for concentrations to reach MCLs in deep, long-screened public-supply wells, however.

Chloroacetanilide Herbicide Metabolites in Wisconsin Groundwater: 2001 Survey Results

A survey of agricultural chemicals in Wisconsin groundwater was conducted between October 2000 and April 2001 to obtain a current picture of agricultural chemicals in groundwater used for private drinking water. A stratified, random sampling procedure was used to select 336 sampling locations. Water from private drinking water wells randomly selected from within the 336 sampling locations was analyzed for 18 compounds including herbicides, herbicide metabolites, and nitrate. This report focuses on the frequency and concentration of chloroacetanilide herbicides and their metabolites. Analysis of data resulted in an estimated proportion of 38+/-5.0% of wells that contained detectable levels of a herbicide or herbicide metabolite. The most commonly detected compound was alachlor ESA with a proportion estimate of 28+/-4.6%. Other detected compounds in order of prevalence were metolachlor ESA, metolachlor OA, alachlor OA, acetochlor ESA, and parent alachlor. Estimates of the mean concentration for the detects ranged from 0.15+/-0.082 microg/L for acetochlor ESA to 1.8+/-0.60 microg/L for alachlor OA. Water quality standards have not been developed for these chloroacetanilide herbicide metabolites. The results of this survey emphasize the need for toxicological assessments of herbicide metabolite compounds and establishment of water quality standards at the state and federal levels.

Distribution and sources of arsenic in the southern high Plains Aquifer, Texas, USA

Arsenic concentrations were compiled for 173 wells in an agricultural region of west central Texas. Wells in the study area produce water from the High Plains (Ogallala) Aquifer. Historically, arsenic compounds were applied to cotton fields in the study area, and they are also present in local rock formations. A geographic information system (GIS) was used to map and evaluate arsenic levels in groundwater. Arsenic was detected in every well, in concentrations ranging from 1.1–171.9 μg/L. Ten observations exceeded 10 μg/L. Several lines of evidence suggest the arsenic came from pesticides instead of local rock formations. These include higher arsenic levels at shallower water table depths, other agricultural chemicals in groundwater, incompatible hydraulic head differentials between the High Plains Aquifer and potential arsenic‐bearing formations, and low arsenic levels in groundwater of potential arsenic‐bearing formations.

Temporal Trends of Selected Agricultural Chemicals in Iowa's Groundwater, 1982–1995: Are Things Getting Better?

Since 1982, the Iowa Groundwater Monitoring (IGWM) Program has been used to sample untreated groundwater from Iowa municipal wells for selected agricultural chemicals. This long-term database was used to determine if concentrations of select agricultural chemicals in groundwater have changed with time. Nitrate, alachlor [2-chloro-2′-6′-diethyl-N-(methoxymethyl)-acetanilide], atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), cyanazine [2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropionitrile)], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] were selected for this temporal analysis of the data. Conclusive temporal changes in frequency of detection and median chemical concentrations were found only for atrazine (decrease) and metolachlor (increase). The greatest temporal chemical changes occurred in the shallowest wells and in alluvial aquifers—both relating to groups of wells generally having the youngest groundwater age. The temporal patterns found for atrazine and metolachlor are consistent with their patterns of chemical use and/or application rates and are suggestive of a causal relation. Only continued data collection, however, will indicate if the trends in chemical concentrations described here represent long-term temporal patterns or only short-term changes in groundwater. No definitive answers could be made in regards to the question of overall improvements in groundwater quality with respect to agricultural chemical contamination and time, due to the inherent problems with the simplistic measurement of overall severity (summation of alachlor + atrazine + cyanazine + metolachlor concentrations) examined for this study. To adequately determine if there is an actual decreasing trend in the overall severity of contamination (improving groundwater quality), the collection of additional water-chemistry data and the investigation of other measures of severity are needed.

Agricultural Chemicals in Groundwater of the Midwestern United States: Relations to Land Use

To determine the relations between land use and concentrations of selected agricultural chemicals (nitrate, atrazine residue [atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) + deethylatrazinc (2-amino-4-chloro-6-isopropylamino-s-triazine) + deisopropylatrazine (2-amino-4-chloro-6-ethylamino-s-triazine)], and alachlor residue [alachlor, [2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide] + alachlor ethanesulfonic acid (alachlor-ESA; 2-[(2,6-diethylphenyl)(methoxymethyl)amino]-2-oxoethanesulfonic acid)] in groundwater, detailed land use information based on accurate measurements from aerial photographs for the 1991 growing season was obtained within a 2-km radius surrounding 100 wells completed in near-surface unconsolidated aquifers in the midwestern USA. The most significant land use factors to the agricultural chemicals examined were: nitrate (amount of irrigated crop production, positive relation), atrazine residue (amount of irrigated crop production, positive relation), and alachlor residue (amount of highly erodible land, inverse relation). The investigation of smaller buffer sizes (size of circular area around sampled wells) proved insightful for this study. Additional land use factors having significant relations to all three agricultural chemicals were identified using these smaller buffer radii. The most significant correlations (correlation maxima) generally occurred at ≤500-m for nitrate and ≥1000-m for atrazine residue and alachlor residue. An attempt to improve the statistical relations to land use by taking hydrologic considerations into account (removing land outside the estimated most probable recharge area from the statistical analysis) was not as successful as anticipated. Only 45% of the nitrate, 32% of the atrazine residue, and 20% of the alachlor residue correlations were improved by a consideration of the estimated most probable recharge area.

Comparability of Large‐Scale Studies of Agricultural Chemical Contamination of Rural Private Wells

AbstractDetection of agricultural chemicals in ground water has prompted numerous studies. Federal, state, and regional studies were conducted in the last 10 years in order to assess the occurrence of agricultural chemicals in ground water. The results of the studies present the number or percentage of samples with agricultural chemicals above the drinking water standard or health advisory levels as well as samples with detections of one or more compounds. Data comparison from one state or region to another are frequently referred to by regulatory and agency personnel involved in water quality and agriculture issues. Unless the history of pesticide use, method of chemical analyses, detection limits, statistical design of the sampling plan, well type, well depth, geology of the formation material, and typical land use around the wellhead are known, such comparisons can be misleading. Reporting the limitations or presenting a disclaimer should be a key element for a study so that “apples and oranges” are not compared.

Nonpoint sources

Nonpoint sources

APPLICATION OF A GEOGRAPHIC INFORMATION SYSTEM TO A LOCAL GROUNDWATER STUDY

Environment Canada, in co-operation with Agriculture Canada, is conducting research studies on agricultural chemicals in groundwater at Sheffield Farm Research Station in the Annapolis-Cornwallis Valley of Nova Scotia. The purpose of this project is to create a digital database for the Research Station by integrating data from several sources. A microcomputer-based geographic information system (GIS) called Spatial Analysis System (SPANS), was evaluated for handling digital data in different formats from several sources.The project involved data transfer between mini- and microcomputer based image analysis and geographic information systems. The results obtained through this geo-database creation and manipulation were multi-faceted and included identifying problems encountered in GIS application, and display of polygonal data, vector data and point data as thematic images. Thematic images generated were topographic maps, water table maps, geological cross-sections, soils maps and water quality maps.The da...

Accounting for Temporal Variations in Large‐Scale Retrospective Studies of Agricultural Chemicals in Ground Water

AbstractGround water studies that require long data collection periods may be affected by temporal changes in ground water chemistry. Seasonal fluctuations in ground water chemistry are particularly apparent in shallow aquifers. Of specific interest is the inclusion of temporal variability in the design of statistical surveys of agricultural chemicals in well water. Statistical treatment of temporal variability involves selecting a probability sample from temporal units. The selection strategy may include repeating the same spatial units in each temporal stratum or choosing an independent sample of spatial units for each temporal stratum. The appropriate strategy depends on the specific study objectives. Failure to account for temporal variability may compromise the validity of study conclusions. An example of a large‐scale retrospective survey designed to estimate temporal averages of water quality across all wells is presented.

Risk‐Based Selection of Monitoring Wells for Assessing Agricultural Chemical Contamination of Ground Water

AbstractMonitoring of water supply wells has long been a responsibility of public health agencies. With the exception of large municipal water supply systems, most monitoring has been bacteriological, and sampling priority and frequency have been governed by the size of the water supply system. Current concerns about the health effects of agricultural chemicals has created a dilemma for public health agencies, because sampling costs for trace organic chemicals are much higher than for bacteriological parameters. A three‐level hierarchical strategy for jointly assessing contamination risk of water supply wells by agricultural chemicals, and prioritizing wells for sampling, is described. At the first level, a determination is made as to data needs and availability, monitoring objectives are defined, and the scope of the monitoring program is established. At the second level, risk or contamination susceptibility factors are identified, and algorithms for quantifying contamination risk as a function of the susceptibility factors are developed. At the third level, the algorithms are calibrated using pilot data, and an optimization scheme for prioritizing additional wells for sampling is developed based on either minimization of the aggregate health risk and risk uncertainty, or on information gained through sampling. The monitoring of Whatcom County, Washington, domestic wells for ethylene dibromide (EDB), a highly toxic soil fumigant whose registration was suspended in 1983 by the U.S. Environmental Protection Agency, is used as a case study for testing of Levels Two and Three of the hierarchy. In the case study, the initial data consisted of EDB concentrations and ancillary data, such as well depth and pumping rate, for 24 wells already sampled. Susceptibility factors were identified, and a Level Three algorithm was used to prioritize the next 10 wells from among 54 additional candidate wells for a second stage of sampling. The sensitivity of the monitoring well selection, and risk‐benefit tradeoff, are evaluated for different monitoring budgets, risk susceptibility parameters, and risk‐benefit tradeoff criteria.SummaryThe design of sampling programs for detection of agricultural chemicals in ground water is a difficult task. A review of ground water pesticide sampling programs that have been undertaken to date indicate that a lack of direction has existed in many past studies. This lack of focus generally has resulted from failure to clearly define sampling program objectives and to relate data collection priorities to those objectives. Even in California, where a very large sampling program for DBCP was undertaken (more than 8000 wells sampled), Holden (1986) reported that due to the lack of specific study objectives, the data obtained were limited in the scope of their applicability. In this paper, a methodology has been described that provides a framework for clear definition of objectives and data needs, enabling efficient design of sampling programs. The framework consists of a three‐level hierarchy. Once study objectives and data needs have been defined at the top level of the hierarchy, specific analytical methods are used (in the second level) to link well contamination probability to certain susceptibility factors and (in the third level) to select wells for sampling in a multistage sampling process.The methodology was applied to a specific problem, the contamination of drinking water in Whatcom County, Washington, by the pesticide EDB. The application study demonstrated the use of available data to estimate the probability of contamination for each well in the study area, and the use of such estimates to guide future sampling as part of a multistage, interactive sampling program. The proposed approach is generally applicable to the problem of ground water contamination by agricultural chemicals. Many pesticides and herbicides are currently of concern because of their potential presence in drinking water. Sampling programs currently being undertaken to study these problems could clearly benefit from structuring of the monitoring design decision process as proposed and demonstrated.

Agricultural Chemicals in Ground Water: Suggestions for The Environmental Protection Agency Strategy

Ground water, a hidden resource whose volume is over 50 times that of the nation's surface water, was once thought to remain forever pure. People had little reason not to believe that the soil would naturally purify water returning to an aquifer. It was not until the late 1970s when the Love Canal and Times Beach incidences redirected public opinion and touched off a nationwide concern for the protection of ground water. In August 1984, the Environmental Protection Agency (EPA) issued a Ground Water Protection Strategy to "provide a common reference for responsible institutions as they work toward the shared goal of preserving, for current and future generations, clean ground water for drinking and other uses, while protecting the public health of citizens who may be exposed to the effects of past contamination."1 More specifically, "EPA will increase efforts to protect ground water from pesticide and nitrate contamination." In response, the EPA's Office of Pesticide Protection reviewed existing information on the extent and causes of pesticide contamination, its potential health hazards, existing statutory authorities, and programs available to aid state policy makers. An increased interest in solving problems associated with pesticides in ground water has resulted in the EPA's current development of a national strategy on Agricultural Chemicals in Ground Water. This strategy will outline the EPA's general course of action in addressing the problem of pesticides in ground water during the next 5 to 10 yr. The purpose of this report is to provide EPA with suggestions to be considered in the formulation of the strategy.

Agricultural chemicals in ground water: Extent and implications

AbstractThe accelerated use of agricultural chemicals over the past 20–30 years has increased production and generally has been profitable, but it has also had an adverse impact on ground water quality in many major agricultural areas. The contamination of ground water, related to nitrogen fertilizers and pesticides, from widespread, routine land application, as well as from point sources has become a serious concern. Ground water contamination also impairs surface water quality. Research, world-wide, has shown increases in NO3-N in ground water concurrent with major increases in N-fertilization. Many shallow ground water supplies now exceed recommended NO3-N drinking water standards. While many sources contribute N into the environment, synthetic fertilizers have become the major component. There are clear economic incentives to improve management; harvested crops often account for less than 50 percent of the purchased fertilizer inputs. Pesticides are appearing in ground water with unanticipated frequency, and while their concentrations are generally below acute toxic levels, many are of concern for possible chronic effects. Such widespread contamination is of real concern because of the potential for long-term and widespread exposure of the public through drinking water. Surveys of farmers indicate a desire to improve management practices and reduce chemical inputs. Promoting the principles of alternative, sustainable agriculture is a necessary element in the resolution of these problems.

Agricultural chemicals in ground water: Preventing contamination by removing barriers against low-input farm management

AbstractAgricultural pesticides and fertilizers have contaminated ground water in areas throughout the U.S. This contamination may adversely affect more than 50 million people. The cost of monitoring to determine the extent of ground water contamination in vulnerable areas is likely to exceed one billion dollars. To reduce the possibility of contamination farmers can adopt “low-input” production methods. Unfortunately, several factors inhibit farmers from adopting low-input methods. These factors include the tendency of farmers to ignore the external costs of agrichemical use, especially environmental damage, the lack of up-to-date information describing low-input farming techniques, and government support programs that indirectly discourage farmers from adopting low-input methods. The federal government can take several steps to eliminate these obstacles. Farm support programs can be changed to eliminate incentives that encourage heavy agrichemical use and to require more stringent environmental compliance to be eligible for program benefits. Taxes can be imposed on agrichemicals to offset their external costs and to provide new funds for research on alternatives. Finally, current agricultural research priorities can be shifted to emphasize low-input production methods.