Pesticides and Pesticide Degradates in Groundwater Used for Public Supply across the United States: Occurrence and Human-Health Context

This
is the first assessment of groundwater from public-supply
wells across the United States to analyze for >100 pesticide degradates
and to provide human-health context for degradates without benchmarks.
Samples from 1204 wells in aquifers representing 70% of the volume
pumped for drinking supply were analyzed for 109 pesticides (active
ingredients) and 116 degradates. Among the 41% of wells where pesticide
compounds were detected, nearly two-thirds contained compound mixtures
and three-quarters contained degradates. Atrazine, hexazinone, prometon,
tebuthiuron, four atrazine degradates, and one metolachlor degradate
were each detected in >5% of wells. Detection frequencies were
largest
for aquifers with more shallow, unconfined wells producing modern-age
groundwater. To screen for potential human-health concerns, benchmark
quotients (BQs) were calculated by dividing concentrations by the
human-health benchmark, when available. For degradates without benchmarks,
estimated values (estimated benchmark quotients (BQE)) were first
calculated by assuming equimolar toxicity to the most toxic parent;
final analysis excluded degradates with likely overestimated toxicity.
Six pesticide compounds and 1.6% of wells had concentrations approaching
levels of potential concern (individual or summed BQ or BQE values
>0.1), and none exceeded these levels (values >1). Therefore,
although
pesticide compounds occurred frequently, concentrations were low,
even accounting for mixtures and degradates without benchmarks.