One or more chemicals were detected in 80 percent of the streams sampled, and 82 of the 95 chemicals were detected at least once.
Generally, these chemicals were found at very low concentrations (in most cases, less than 1 part per billion).
Mixtures of the chemicals were common:
75 percent of the streams had more than one
50 percent had 7 or more
34 percent had 10
RESULTS:
The most frequently detected chemicals (found in more than half of the streams) were:
Coprostanol (fecal steroid)
Cholesterol (plant and animal steroid)
N-N-diethyltoluamide (insect repellent)
Caffeine (stimulant)
Triclosan (antimicrobial disinfectant)
Tri (2-chloroethyl) phosphate (fire retardant)
4-nonylphenol (nonionic detergent metabolite).
Steroids, nonprescription drugs, and insect repellent were the chemical groups most frequently detected.
Detergent metabolites, steroids, and plasticizers generally were measured at the highest concentrations.
Human and environmental effects:
Knowledge of the potential human and environmental health effects of these 95 chemicals is highly varied.
Drinking-water standards or other human or ecological health criteria have been established for 14.
Measured concentrations rarely exceeded any of the standards or criteria. Thirty-three are known or suspected to be hormonally active. 46 are pharmaceutically active.
Little is known about the potential health effects to humans or aquatic organisms exposed to the low levels of most of these chemicals or the mixtures commonly found in this study.