One Time Testing of Iowa Regulated Drinking Water Supplies

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Project Period: 
1986 to 1987

In 1986 the Iowa General Assembly passed House File 2303. This legislation mandated that the Iowa Department of Natural Resources (IDNR) must develop and implement a one-time analytical testing of the finished water from Iowa's publicly and privately owned water systems for 35 pesticide compounds and 35 volatile organic contaminants (VOC). The University Hygienic Laboratory (UHL) provided all analytical services to this program which ran from November 1986 to November 1987.

Eight hundred and fifty-six public water systems were tested. One hundred and twenty-five tested positive for one or more pesticides. Five hundred and fifty tested positive for one or more synthetic organic compounds. No measurable concentrations of pesticides or volatile organic chemicals were found in 279 systems. A few water systems had pesticides or volatile organic chemical levels that exceeded U.S. Environmental Protection Agency health advisories or maximum contaminant levels, but contaminant levels high enough to cause an acute health risk were not observed in this study.

The pesticides most commonly found were atrazine, cyanazine (Bladex), alachlor (Lasso), metolachlor (Dual), and 2,4-D. The most frequently found volatile organic chemicals belong to a group called trihalomethanes (THMs). THMs are formed during disinfection when chlorine reacts with organic matter in the water. Para- and meta-xylene, measured as a single compound, was the second most abundant VOC observed.

The following are the most significant findings of this one time testing:

  • Surface water systems have the greatest potential for pesticide contamination.
  • The shallower ground water sources have a greater potential for contamination by pesticides and VOCs.
  • A seasonal trend in pesticide occurrences in water sources was not observed, with the exception of 2,4-D found at low levels.
  • The frequency of appearance and concentration of trihalomethanes in ground water systems serving small municipalities was unexpected.

For a copy of this report, contact the University Hygienic Laboratory at (319) 335-4500.