Electronic Supplement

Organic Wastewater Contaminants: Methods and Results

Methods of Sample Collection and Analyses

A reconnaissance survey of organic wastewater contaminants (OWCs) in the upper Merced River, the South Fork of the Merced River, and upper Tuolumne River was performed during low-flow conditions in August-October 2006. Surface-water samples were collected for OWCs at six sites during August-September 2006, and the sampling was repeated during October 2006 (Table 1 in main text of manuscript). In addition, one new site was sampled during October 2006. Sites included those upstream from heavily used sections of the rivers (HAPI, SFSB), those just downstream from areas of high visitor use (MRYL, SFWC), and those downstream from sewage treatment plants (FRST, TRBC)(Fig. 1 in main text of manuscript). Site CNCR was selected due to its proximity to a High Sierra Camp.

To minimize potential contamination, field personnel were instructed to avoid use of insect repellant, fragrances, tobacco, and caffeinated products prior to and during OWC sampling. Samples for OWC analyses were collected directly from the river along a well-mixed reach in a pre-cleaned glass syringe. At each field site, 600 ml of sample water were passed through pre-cleaned solid-phase extraction (SPE) cartridges. OWCs were extracted from the SPE cartridges in the laboratory using continuous liquid-liquid extraction (Zaugg et al. 2006). Sixty-eight compounds were analyzed at the USGS National Water Quality Laboratory (NWQL), Lakewood, Colorado by capillary-column gas chromatography/mass spectrometry (Zaugg et al. 2006; NWQL schedule 1433). It was anticipated that OWC concentrations would be low; thus, a special large-volume injector was used to increase the sensitivity and lower the detection limit by approximately one order of magnitude compared to the standard analytical method (NWQL Schedule 1433). Surrogate compounds were added to each sample to monitor recovery and method performance. Laboratory and field blanks were used to assess potential contamination; reported sample concentrations were not blank adjusted. Concentrations of OWCs between the detection limit and the limit of quantification (concentration of the lowest standard in the analytical run) were qualified with an “E” (estimated) to indicate that they were non-quantitative. Additionally, 15 compounds are always reported from the NWQL as “E” due to unacceptably low-biased recovery or highly variable method performance, unstable instrument response, reference standards prepared from technical mixtures, or chronic blank contamination (detections in >10% of blanks) ( accessed 3/1/2009).

Results

Concentrations of all detected OWCs were low, with no concentrations exceeding 1 µg L-1 (Table ESM 3). Ninety-eight percent of the reported concentrations of OWCs were below the limit of quantification.

Although there were a relatively high number of detections of OWCs in the surface-water samples compared to some previous studies (Focazio et al. 2008; Kolpin et al. 2002), this was partly due to the low detection limits of the analytical method that was used in the present study. By using a special large-volume injector, detection limits were approximately ten times lower than those normally obtained using NWQL Schedule 1433. In almost all cases, concentrations in samples were similar in magnitude to those measured in blanks.

Several of the OWCs with the highest reported concentrations, including diethylhexyl phthalate, diethyl phthalate, and para-Cresol, were detected in the blanks at concentrations near the low end of the range of the environmental samples, and thus may reflect false positives. Acetophenone and phenol have been commonly found in blanks in previous studies, and results for these analytes need to be interpreted with caution (Focazio et al. 2008).

The OWCs were divided into 16 groups based on their most common uses (Focazio et al. 2008; Kolpin et al. 2002). The most commonly detected OWCs included plant and animal steroids, plasticizers, and non-ionic detergent metabolites (Fig. ESM 1). These results are consistent with those from reconnaissance surveys of OWCs in drinking-water sources and in the vicinity of wastewater treatment facilities (Focazio et al. 2008; Kolpin et al. 2002). As in the reconnaissance surveys, the naturally occurring steroids cholesterol and beta-Sitosterol were detected in a high percentage of samples (100 and 92% of samples, respectively). In contrast, 3-beta-coprostanol, which is another biogenic steroid and fecal indicator, was detected in 18% of samples in the drinking-water survey and 86% of samples in the wastewater survey, but was detected in only one sample (8%) in the present study. Other analytes that were relatively frequently detected in the reconnaissance surveys, but seldom detected in this study, included 1,7 dimethylxanthine (caffeine metabolite) and cotinine (nicotine metabolite). Although caffeine was detected in 92% of samples in the present study, concentrations were very low (≤0.007 µg L-1; Fig. ESM 1). N,N-diethyl-meta-toluamide (DEET), which is the active ingredient in commonly used insect repellants, was detected in 100% of samples; however, only two samples had concentrations above the quantitation limit of 0.04 µg L-1 (Fig. ESM 1).

Although there were insufficient samples to perform meaningful statistical tests, there did not appear to be any strong spatial patterns in concentrations of OWCs; samples collected downstream from the wastewater treatment plants did not have appreciably higher concentrations than those collected upstream from the plants or areas of high visitor use, although few concentrations were above the limit of quantification (Table 3 in electronic supplement).

Bibliography

Focazio, M. J., D. W. Kolpin, K. K. Barnes, E. T. Furlong, M. T. Meyer, S. D. Zaugg, L. B. Barber, and E. M. Thurman (2008). A national reconnaissance for pharmaceuticals and other organic wastewater contaminants in the United States -- II) Untreated drinking water sources. Science of the Total Environment, 402, 201-216.

Kolpin, D. W., E. T. Furlong, M. T. Meyer, E. M. Thurman, S. D. Zaugg, L. B. Barber, and H. T. Buxton (2002). Pharmaceuticals, hormones, and other organic wastewater contaminants in U.S. streams, 1999-2000: A national reconnaissance. Environ. Sci. Technol, 36, 1202-1211.

Zaugg, S. D., S. G. Smith, and M. P. Schroeder (2006). Determination of wastewater compounds in whole water by continuous liquid-liquid extraction and capillary-column gas chromatography/mass spectrometry. US Geological Survey Techniques and Methods, Book 5, Chapter 4, U.S. Geological Survey, Denver, available online at