Compounds of Emerging Concern in the San Antonio River Basin, Texas, 2011–12

A compound of emerging concern is, in the U.S. Geological Survey's definition, any synthetic or natural chemical, or any microorganism, that is not usually monitored in the environment but could get into it and cause known or suspected harm to ecosystems or human health. Many are known endocrine disruptors or possible human carcinogens. How they affect people and aquatic life, alone or in combination, is still poorly understood, and most are unregulated — but data on where they occur, and how much, are growing and can inform water treatment and management.

The San Antonio River. Photograph from the USGS fact sheet.

The study

San Antonio and its neighbours in Bexar County are among the fastest-growing cities in the nation, and new homes and businesses change how rain runs off and are likely to add chemicals to streams. With the San Antonio River Authority, the USGS sampled 20 sites in the San Antonio River Basin in 2011–12 for three groups of compounds:

• wastewater compounds — 54 analysed;
• pharmaceuticals — 13;
• steroidal hormones and sterols — 17 hormones and 4 sterols.

Samples came from three synoptic rounds, in which many sites are sampled at once for a snapshot of the whole basin: the first two at the same 12 sites, the third at seven sites added later. The rural Ecleto site had no flow during those rounds and was sampled separately. Overall, concentrations were low, generally near or below the laboratory reporting level.

Sampling sites (EC01–EC20), wastewater discharge sites (WW01–WW17) and, from the first round (March–May 2011), the total concentration and mix of wastewater compounds at each site. USGS.

Wastewater compounds

These come from treated household and industrial wastewater, mostly through discharges from wastewater treatment plants and water recycling centers, and to a lesser degree from septic seepage, leaking sewers and urban runoff. They were found more often than the other two groups: thirty-two of the 54 were detected at least once, most often personal-use compounds, industrial compounds, and flame retardants and plasticizers.

• The flame retardants tris(2-chloroethyl) phosphate and tris(dichloroisopropyl) phosphate — possible endocrine disruptors used in clothing, mattresses and sofa cushions — were the most frequent, measurable in 28 of 33 samples.
• The highest concentration was of the fragrance HHCB (hexahydrohexamethyl-cyclopentabenzopyran): up to 1.90 micrograms per liter (µg/L), from an estimated 0.006.
• Next was 5-methyl-1H-benzotriazole, a corrosion inhibitor in dishwasher detergents, de-icing fluids, antifreeze, brake fluids, industrial coolants and metal-cutting fluids: an estimated 0.1 to 1.4 µg/L.
• Every other wastewater compound was below 1.0 µg/L or not detected.

Detections of each wastewater compound in 33 samples. By subclass: flame retardants and plasticizers 100, personal-use compounds 88, industrial compounds 62, pesticides 19, disinfection compounds 13, polycyclic aromatic hydrocarbons 11, detergent metabolites 9. USGS.

Pharmaceuticals

Medicines given to people or animals reach the environment in treated wastewater, by direct excretion, and in discharges from drug factories. Their active ingredients worry researchers because of the quantities released, their effects on hormones, and the risk of spreading bacterial resistance. 4 of the 13 were found in the 34 samples:

• carbamazepine, an anticonvulsant that breaks down slowly and survives water treatment — the most frequent, in 24;
• the antibiotic sulfamethoxazole, in 15;
• dehydronifedipine, the main breakdown product of the heart drug nifedipine, in 13;
• the antihistamine diphenhydramine, the one non-prescription drug, in 6.

Hormones and sterols

Steroidal hormones and sterols are natural chemicals of animal and plant metabolism; people also use synthetic ones such as anabolic steroids and birth-control compounds. Through excretion and wastewater they reach streams, raising concern for freshwater life. Eight were detected. Estrone, a breakdown product of 17-beta-estradiol, was the estrogen-related compound found most often (9 of 34 samples). The four sterols — plant beta-sitosterol and beta-stigmastanol, animal 3-beta-coprostanol and cholesterol — were detected 41 times in 34 samples, cholesterol most often (19).

Detections of hormones and sterols in 34 samples: natural androgens 2, natural estrogens 14, animal sterols 21, plant sterols 20. USGS.

The sheet counts the steroidal compounds two ways: 17 hormones and 4 sterols analysed, and "8 of 17 steroidal hormones and sterols" detected.

Where they turned up

• In the 2011 rounds, sites downstream of treatment-plant and recycling-center outfalls had more detections and higher totals than other sites. The most, and the highest concentrations, were at San Antonio River at Elmendorf (EC13), downstream of San Antonio.
• Urban streams with no large wastewater source upstream still carried 1,4-dichlorobenzene, p-cresol, phenol, the fragrances AHTN and HHCB, tributyl phosphate, triethyl citrate and triphenyl phosphate — so many of these compounds reach streams in built-up areas without treated wastewater.
• At the rural Ecleto site, wastewater compounds show they can reach rural streams too, in runoff or seepage from septic systems. Its hormones and sterols most likely came from cattle waste, since the site lies in rangeland that receives no runoff from San Antonio.
• Few pharmaceuticals appeared in streams without wastewater outfalls upstream, and lower levels at the farthest downstream sites suggest some dilution or natural breakdown along the way.

Sources

• Rebecca B. Lambert and Stephen P. Opsahl, Compounds of Emerging Concern in the San Antonio River Basin, Texas, 2011–12, USGS Fact Sheet 2016–3071, November 2016, prepared with the San Antonio River Authority. https://doi.org/10.3133/fs20163071
• Full study: Stephen P. Opsahl and Rebecca B. Lambert, USGS Scientific Investigations Report 2013–5200. https://doi.org/10.3133/sir20135200
• Corrected: the sheet spells "1,4-dicholorobenzene" and lists "dishwater" detergents; the compound is 1,4-dichlorobenzene and the detergents are for dishwashers.
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.