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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5027

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Summary

During 2000–2005, ultra low detection level analyses for 86–198 pesticides in 119 water samples collected from sites in the lower mainstem Clackamas River, its tributaries, and in pre- and post-treatment (source and finished) drinking-water from the study water-treatment plant—one of four drinking-water treatment plants that draw from the lower Clackamas River. In all, 63 pesticide compounds: 33 herbicides, 15 insecticides, 6 fungicides, and 9 pesticide degradates were detected in samples collected during storm and nonstorm conditions. Fifty-seven pesticides or degradates were detected in the tributaries (mostly during storms), whereas fewer compounds (26) were detected in samples of source water from the lower mainstem Clackamas River, with fewest (15) occurring in drinking water.

The two most commonly detected pesticides were the triazine herbicides simazine and atrazine, which occurred in about one-half of samples. Deethylatrazine (a degradate of atrazine) commonly was detected along with atrazine in about 30 percent of samples. The active ingredients in the common household herbicides RoundUP™ (glyphosate) and Crossbow™ (triclopyr and 2,4-D) also were frequently detected together. These three herbicides often made up most of the total pesticide concentration in tributaries throughout the study area.

Pesticides were most prevalent in the Clackamas River during storms, and were present in all storm-runoff samples (collected from Deep, Richardson, Rock, Sieben, Carli, and Cow Creeks)—averaging 10 pesticides per sample from these streams. Two tributaries of Deep Creek (North Fork Deep and Noyer Creeks) contained 17–18 pesticides each during a storm in May 2005. Streams draining predominantly forested basins such as Eagle and Clear Creeks contained fewer pesticides (2–5 pesticides), and were not sampled after 2000.

Many of the highest insecticide concentrations in the tributaries exceeded U.S. Environmental Protection Agency (USEPA) aquatic-life benchmarks, including diazinon, chlorpyrifos, p,p΄-DDE, and azinphos-methyl. Nearly one-quarter of the tributary samples had at least one pesticide that exceeded an aquatic-life benchmark. Azinphos-methyl was detected only once during the study (in Doane Creek) at a concentration of 0.21 μg/L, which exceeded the State of Oregon and USEPA aquatic-life benchmarks (0.01 μg/L) by a factor of about 20. Doane Creek drains high density nursery land in the North Fork Deep Creek basin, and was highly turbid (120 Nephelometric Turbidity Ratio Units) during sampling.

Concentrations of pesticides in the Clackamas River were much lower than those in the tributaries owing to greater dilution (higher streamflow) derived from the mostly forested upper drainage basin. In all, 26 pesticides and degradates were detected in the Clackamas River mainstem or in source water from the study water treatment plant intake. At least 1 pesticide was detected in 22 of 34 (65 percent) source water samples, with an average of 2–3 pesticides per sample (1 source water sample collected during a September 2005 storm contained 13 pesticides). Although none of the USEPA aquatic-life benchmarks were exceeded in the mainstem, concentrations of the insecticide chlorpyrifos exceeded non-USEPA benchmarks from the NAS/NAE and Canada.

In all, 15 pesticides were variously detected in the 18 samples of finished drinking water from the selected water-treatment plant on the lower river, although concentrations of some pesticides in finished drinking water reported here may differ from other treatment plants in the lower Clackamas River because differing treatment processes were not investigated during the study. Although 98 percent of the 1,790 individual pesticide analyses of drinking water were below detection, one or more pesticides were detected in 60 percent of finished water samples. The four most common were herbicides, diuron, simazine, dacthal, and hexazinone, which occurred in 2–4 samples each. Other detected compounds included 2,4-D, atrazine, deethylatrazine, metolachlor, trifluralin, pronamide, and metsulfuron-methyl (all herbicides), the insect repellent DEET, plus three others. During the September 2005 storm, diazinon-oxon (a degradate of the organophosphate insecticide diazinon), ethoprop (another orthophosphate insecticide), propiconazole (a fungicide), and three other pesticides were detected in finished drinking water. As many as nine pesticide compounds occurred in a single sample, 9 days following a storm in May 2005.

All pesticide concentrations in finished water occurred at trace levels far below USEPA Maximum Contaminant Levels (MCLs) for regulated contaminants, and USGS human Health Based Screening Levels (HBSLs) for unregulated contaminants. Three compounds (diazinon-oxon, deethylatrazine [CIAT], and DEET [an insect repellent]), however, do not have human-health benchmarks available for comparison and were not included in this screening-level assessment.

The highest measured pesticide concentration in finished drinking water (0.18 micrograms per liter of the herbicide diuron) occurred 9 days following a storm in May 2005. This value is 11 and 1,100 times lower than the low-HBSL and high-HBLS benchmark, respectively, for diuron and would not be expected to cause adverse effects if water with such a concentration were to be ingested over a lifetime. Pesticide concentrations in finished drinking water may be higher than actual concentrations in the distribution system because finished water samples were preserved with a dechlorinating agent to stop the breakdown of pesticides by chlorine prior to laboratory analysis. Concentrations of readily degradable compounds could be less at customers’ taps, depending on the amount of time water is in contact with chlorine in the distribution system. Further study on the water treatment processes and their ability to remove pesticides could help evaluate potential treatment options.

The aquatic-life and human-health benchmarks currently do not account for simultaneous exposure to multiple pesticides and degradates. Benchmarks are derived from toxicological experiments on individual compounds and do not reflect the totality of exposure that organisms in these streams experience. In this study, as many as 18 pesticides were detected in a single sample (from upper Noyer Creek), and it is difficult to determine the cumulative effect of such a mixture. Future studies could examine the potential for physiological interactions that may occur among pesticides and other organic or inorganic chemicals that may be present in the river or in finished drinking water.

Of the 51 current-use pesticides detected in the basin, 47 have uses associated with nursery and floriculture crops (29 herbicides, 12 insecticides, and 6 fungicides). About one-half of the pesticides detected in the Clackamas River basin also are commonly used on lawns and landscaping in urban areas (57 percent), on golf courses (49 percent), applied along fences, roads, and other right-of-ways (45 percent). Although not specifically examined in this study, 14 percent of the pesticides may be used on forestland, and considering the large amount of forest acreage in the basin, applications to State or private forestland also may be important. Pesticide use on Federal land in the basin is rare, although applications have been done in the past.

In a previous report on pesticides in the Clackamas River basin, it was estimated that as much as one-half of the agricultural pesticide use could be on nursery, floriculture, and greenhouse crops, with lesser amounts applied to pastureland, Christmas trees, alfalfa and hay fields, hazelnut orchards, and grass seed fields. Findings from the current study also suggest that nursery and greenhouse operations could be a significant source of pesticides to the lower Clackamas River. Future studies could develop source reduction strategies and best management practices in the Deep Creek and Rock Creek drainage basins, for example, to minimize pesticide transport from nurseries in these basins.

The diverse land use in the study area and unpredictable water management (pumping, irrigation, collection, and release) make it challenging to identify pesticide sources. Data collected for Oregon’s Pesticide Use and Reporting System (PURS) will be at a coarse scale, making it difficult, if not impossible, to locate sources within the Clackamas River basin. Pesticide applications in the Clackamas River basin, for example, will likely be incorporated into a larger report for the entire Willamette River basin. The PURS data will be useful, however, for identifying potentially important chemicals not currently being analyzed. Only a small fraction of the approximately 11,000 pesticide products registered for use in Oregon were analyzed during this study, which makes pesticide-use data especially helpful for developing monitoring plans. Urban-use surveys conducted as part of the PURS also may provide data on the types and amounts of pesticides used in urban areas. Urban use could be significant considering that the 3 streams draining the highly urbanized and industrial northwestern part of the basin (Cow, Carli, and Sieben Creeks) contained 11–24 pesticides each.

Given their frequent and widespread occurrence, especially during storms, pesticides have the potential to affect aquatic life and the quality of drinking water derived from the lower river. The dynamic nature of pesticide runoff, and potentially highly variable concentrations of pesticides during storms, makes it difficult to determine the chronic and acute exposure levels in the tributaries and mainstem Clackamas River. Future studies could include multiple samples collected during and after a storm to determine how long concentrations are elevated. Future studies also could examine the transport and fate of pesticides from application areas to waterways, evaluate trends in concentrations over time, evaluate the potential cumulative effects of pesticide mixtures on aquatic life, and evaluate water-treatment options that might reduce pesticide concentrations in finished drinking water.

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