|Organochlorine Pesticides in the Johnson Creek Basin, Oregon, 1988-2002|
|By Dwight Q. Tanner and Karl K. Lee|
|Scientific Investigations Report 2004-5061|
|Prepared in Cooperation with the City of Portland, the City of Gresham, the City of Milwaukie, Clackamas County, and Multnomah County|
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Organochlorine pesticides were detected in unfiltered samples from Johnson Creek that were collected during a storm in March, 2002. Total DDT (the sum of DDT and its metabolites), as well as dieldrin, potentially exceeded Oregon chronic, freshwater criteria at all four Johnson Creek stream-sampling sites. The total DDT criterion was also potentially exceeded at a storm drain at SE 45th Avenue and Umatilla Street.
The concentration of total DDT in water samples has decreased by an order of magnitude since previous sampling was done on Johnson Creek in 19891990. This decrease was probably due to the movement of these compounds out of the basin and to degradation processes. Concentrations and loads of the organochlorine pesticides were largest at the most upstream sampling site, Johnson Creek at Palmblad Road, which has historically been primarily affected by agricultural land cover. Concentrations and loads were smaller at downstream locations, and there were only a few detections from storm drains.
For the purposes of assessing trends in total DDT concentration in Johnson Creek, data for total suspended solids (TSS) were examined, because TSS is often correlated with DDT concentrations, and TSS data are collected routinely by regulatory agencies. As an intermediate step, linear regression was used to relate TSS (measured in the recent study) and turbidity (measured both in the earlier and in the recent studies). For 77 samples, TSS (in mg/L [milligrams per liter]) = 0.88 x Turbidity (in nephleometric turbidity units). The r2 value was 0.82.
The TSS concentration (measured, or estimated by the regression) was compared to the concentration of total DDT using linear regression. The TSS concentration associated with meeting the Oregon water-quality criterion for total DDT was 15 to 18 mg/L in the lower and middle part of the basin and 8 mg/L in the upper reaches of the basin. This TSS/DDT relationship is based on only one storm and may not be valid for other conditions of streamflow and runoff. Dieldrin concentration was not well correlated with TSS.
Organochlorine compounds also were detected in significant concentrations in Kelley Creek, an important tributary to Johnson Creek, but quality-control considerations made it difficult to interpret some of the data. It does appear, however, that some of the metabolites of DDT were positively associated with TSS. The high concentrations of the DDT metabolites and dieldrin were correlated with agricultural areas.
Purpose and Scope
Study Area Description
Study Design and Methods
Sample Collection and Analysis
Hydrologic Conditions during Storm Sampling
Occurance of Organochlorine Pesticides
and Compliance with Criteria
Loads of Organochlorine Pesticides
Relation of Total Suspended Solids to Turbidity
Relation of Organochlorine Pesticides
to Total Suspended Solids
Organochlorine Pesticides in Kelly Creek
Implications for Future Study
Summary and Conclusions
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Last modified: Thursday, December 01 2016, 08:06:54 PM