Finding minimal herbicide concentrations in ground water? Try Looking for their degradates

Extensive research has been conducted regarding the occurrence of herbicide s in the hydrologic system, their fate, and their effects on human health a nd the environment. Few studies, however, have considered herbicide transfo rmation products (degradates). In this study of Iowa ground water, herbicid e degradates were frequently detected. In fact, herbicide degradates were e ight of the 10 most frequently detected compounds. Furthermore, a majority of a herbicide's measured concentration was in the form of its degradates - ranging from 55 to over 99%. The herbicide detection frequencies and conce ntrations varied significantly among the major aquifer types sampled. These differences, however, were much more pronounced when herbicide degradates were included. Aquifer types presumed to have the most rapid recharge rates (alluvial and bedrock/karst region aquifers) were those most likely to con tain detectable concentrations of herbicide compounds. Two indirect estimat es of ground-water age (depth of well completion and dissolved-oxygen conce ntration) were used to separate the sampled wells into general vulnerabilit y classes (low, intermediate, and high). The results show that the herbicid e detection frequencies and concentrations varied significantly among the v ulnerability classes regardless of whether or not herbicide degradates were considered. Nevertheless, when herbicide degradates were included, the fre quency of herbicide compound detection within the highest vulnerability cla ss approached 90%, and the median total herbicide residue concentration inc reased over an order of magnitude, relative to the parent compounds alone, to 2 mu g/l. The results from this study demonstrate that obtaining data on herbicide degradates is critical for understanding the fate of herbicides in the hydrologic system. Furthermore, the prevalence of herbicide degradat es documented in this study suggests that to accurately determine the overa ll effect on human health and the environment of a specific herbicide its d egradates should also be considered. (C) 2000 Elsevier Science B.V. All rig hts reserved.