Organic Waste Compounds in Milwaukee-Area Streams: What USGS Found

The study

During 2006–9 the USGS and the Milwaukee Metropolitan Sewerage District (MMSD) studied organic waste compounds (OWCs) in Milwaukee-area streams — how often they occur, in what amounts, where, and how toxic they are — to help watershed managers set priorities.

What OWCs are: ingredients and by-products of everyday farm, industrial and household products. The study grouped 69 compounds into 15 classes: antioxidants, dyes and pigments, fire retardants, polycyclic aromatic hydrocarbons (PAHs), plasticizers, fuels, solvents, herbicides, insecticides, antimicrobial disinfectants, detergent metabolites, flavors and fragrances, nonprescription drugs, sterols and miscellaneous.

How they get in: urban and farm runoff, industrial discharges to air or water, leaching from unlined landfills, wastewater-treatment plants, combined sewer overflows, and leaking septic systems and sewers. Many are toxic at high levels or can disrupt hormones; even low levels can harm aquatic life exposed over whole lifetimes and generations, and mixtures can strengthen the effects.

Sampling: 12 sites, with three sample types — stream water at normal flow (base flow), water within the streambed (pore water) and streambed sediment. Four sites, from least to most urban, were also sampled during storms: the Milwaukee River near Cedarburg (MRC), Oak Creek at South Milwaukee (OSM), the Menomonee River at Wauwatosa (MRW) and the Kinnickinnic River at South 11th Street, Milwaukee (KRM). Water was tested for 69 compounds, sediment for 57.

The twelve sampling sites and a summary of what was found at each. USGS.

How often

• All 196 samples contained at least one compound — up to 41 in a single sample.
• 64 of the 69 compounds were detected at least once.
• Base-flow samples had the fewest (a median of 12 compounds); stormflow, pore-water and sediment samples had about twice as many.
• PAHs were found most often — in 100 percent of stormflow, pore-water and sediment samples and 80 percent of base-flow samples — followed by insecticides, herbicides and dyes/pigments.

How often each class was found, and its highest concentration, at the four storm-sampled sites. USGS.

How much

• PAHs and herbicides reached the highest concentrations.
• Most compounds were more concentrated in stormflow and pore water than in base flow — especially PAHs, dyes/pigments and solvents. Storm concentrations were at least 2 times base-flow levels for 23 compounds and at least 10 times for 5. Storm runoff and sewage leaks during storms look like important sources.

Human wastewater indicators. A set of 20 compounds that point to leaking sewers and septic systems — all fire retardants and detergent metabolites, most fragrances, and the disinfectant triclosan — turned up in 100 percent of stormflow and pore-water samples, 79 percent of base-flow and 89 percent of sediment samples. Totals generally rose with urban area, and were highest at the Kinnickinnic.

Potentially toxic amounts

25 of the 69 compounds have aquatic-toxicity benchmarks — levels above which harm is possible (not legal standards). 13 of the 25 were exceeded.

• PAHs exceeded benchmarks most — in up to 93 percent of sediment samples, and at up to 1,024 times the benchmark.
• Some plasticizers, fuels, disinfectants and detergent metabolites also exceeded them.
• Seven compounds exceeded benchmarks in both water and sediment, suggesting they wash in and settle into the streambed.
• Benchmarks judge single compounds over 10 days or less; these streams carried mixtures of 20 to 40 compounds for weeks or months, so the benchmarks may understate the risk.

Featured result: PAHs and urban storms

PAHs come from vehicle and power-plant emissions, tire particles, motor oil, creosote, roofing tar and coal-tar pavement sealants. They break down slowly and build up in sediments.

• In stormflow, PAH levels tracked the share of the basin that is urban: the median at the Kinnickinnic was 83 times that at the least urban site.
• PAHs were potentially toxic at 3 of 4 stormflow sites, 4 of 9 pore-water sites and 7 of 9 sediment sites — but rarely in base flow. They enter with urban storm runoff and collect in the streambed.

PAH potential toxicity in base flow (top) and stormflow (bottom), least to most urban. Above the dashed line, samples are potentially toxic. USGS.

Urbanization and storms, overall: roads and roofs send runoff into storm sewers instead of the ground, and sewers and septic systems overflow in storms. Urban sites had more detections, higher concentrations and more benchmark exceedances than rural ones; storm concentrations were up to 10 times base-flow levels, and storm detection rates 1.3 to 2.0 times higher; the Kinnickinnic was highest of all.

Sources

Based on Austin K. Baldwin, Steven R. Corsi, Christopher Magruder, Matthew Magruder and Jennifer L. Bruce, "Organic Waste Compounds as Contaminants in Milwaukee-Area Streams," U.S. Geological Survey fact sheet, summarizing USGS Scientific Investigations Report 2013–5104; a work of the United States government in the public domain. The map and charts are taken from the fact sheet's PDF.