Pesticides in Eastern North Carolina Rural Supply Wells: Land Use Factors and Persistence

Abstract

Water samples were collected from 171 rural domestic well supplies in eastern North Carolina and analyzed for eight pesticides. Information on borehole depth, well‐easing depth, distance to nearest pesticide mixing area, types of pesticides used, and distance to nearest field application was obtained for each site. Four herbicides [alachlor, 2‐chloro‐2′‐6′diethyl‐N‐(methoxymethyl)‐acetanilide; atrazine, 2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine; metolachlor, 2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl) acetamide; trifluralin, α,α,α‐trifluoro‐2,6‐dinitro‐N,N‐dipropyl‐p‐toluidine] were detected in the samples, with detection frequencies of 8.8, 8.2, 3.6, and 1.8%, respectively. About 15% of the samples contained at least one of these herbicides, with resampling indicating persistence throughout the year. Only alachlor concentrations were in excess of maximum contaminant levels (MCLs; 2.0 μg L−1) or Health Advisory Levels (HALs; 0.4 μg L−1) established by the U.S. Environmental Protection Agency (USEPA). Neither atrazine nor alachlor detection exhibited statistical correlation with well depth, although both were rarely detected in wells >100 feet deep. Atrazine concentrations and detection frequencies did not correlate with distance to nearest application site, while alachlor had a significantly greater detection frequency for wells further from the nearest application site. For nearly one‐half of the wells with detectable atrazine and alachlor, there was no reported usage of either herbicide on the same farm during the previous three years, possibly indicating herbicide transport in groundwater or long times before degrading. No statistically significant relationships were observed between the presence of alachior or atrazine, and distance from the well to the nearest pesticide handling and storage area. Although inconclusive by itself, this indicates that at least some contamination originated from other than point‐source spills. Nitrate‐N concentrations in well water were poor predictors for atrazine and alachlor presence in this study.

Direct assessment of groundwater vulnerability from single observations of multiple contaminants

“…The data used in this study comes from regional surveys that encompasses a large part of US agriculture and these could be extended to other regions from the many studies available in the literature [e.g., Maas et al, 1995]. However, the Bayesian framework within which these methods were developed and the observation that vulnerabilities can be described as a beta distribution allow results to be used in a flexible manner.…”

“…Close [1993b] gave a validation for the DRASTIC method, while Maas et al [1995] showed it to be a poor predictor of vulnerable groundwater regions. The UK vulnerability system shows no statistically significant relationship with measured groundwater contamination [Worrall, 2003].…”

Présence de Pesticides dans l’Eau Souterraine en Milieu Agricole : Étude Pilote du Bassin Versant de la Rivière Châteauguay

“…De plus, les caractéristiques physicochimiques du chlorpyrifos, soit sa faible solubilité dans l'eau, ou sa tendance à s'adsorber fortement aux particules, font que ce pesticide est généralement considéré comme peu mobile dans l'environnement et peu susceptible de contaminer les eaux souterraines (Laverdière et Grégoire, 2002). Aux États-Unis, une situation similaire est rapportée par Maas et al (1995) pour plusieurs puits de producteurs agricoles de la région est de l'état de Caroline du Nord où les herbicides atrazine et alachlore ont été détectés sans qu'il n'y ait d'usage récent de ces produits à proximité des puits. Dans les conditions de vulnérabilité de l'eau souterraine de cette région, les auteurs avancent les hypothèses d'un usage ancien des produits, d'une source de contamination plus éloignée, ou de possibles rotations des cultures près de ces puits.…”

The vulnerability of groundwater to pesticide contamination estimated directly from observations of presence or absence in wells

“…Where DRASTIC has been validated on the basis of the occurrence of pesticide (Close, 1993b) and nitrate with the highest vulnerability class (Navulur and Engel, 1998), but was shown to be a poor predictor of vulnerable groundwater regions (Maas et al, 1995;Barbash and Resek, 1996;Garrett et al, 1989;Koterba et al, 1993;US Environmental Protection Agency, 1993). To be most effective DRASTIC required calibration against real groundwater observations (Rupert, 2001).…”