Thousands of chemicals serving a variety of human needs flood into sewage treatment plants once their use life has ended. Many belong to a class of chemicals known as CECs (for chemicals of emerging concern), which may pose risks to both human and environmental health. Arjun Venkatesan, a recent doctorate¹ and Rolf Halden, professor and director of the Center for Environmental Security at Arizona State University's Biodesign Institute, have carried out meticulous²（小心翼翼的） tracking of many of these chemicals.

 

In a study appearing today in the Nature Publishing Group journal Scientific Reports, both authors outline a new approach to the identification of potentially harmful, mass-produced chemicals, describing the accumulation in sludge（烂泥） of 123 distinct CECs.

 

Ten of the 11 chemicals found in greatest abundance in treated municipal sludge or biosolids were high-production volume chemicals, including flame-retardants, antimicrobials and surfactants（表面活性剂）.

 

The study shows a strong overlap³ between chemicals found in biological samples taken from the human population and those detected in municipal biosolids. These findings suggest that analysis of sludge may provide a useful surrogate for the assessment⁴ of human exposure and bioaccumulation of potentially hazardous⁵ substances.

 

According to Venkatesan, "presence of CECs in sewage suggests that consumers already may get exposed to these chemicals prior to their discharge into sewage, suggesting a need for human biomonitoring and risk assessment of these priority chemicals."

 

Prioritizing the thousands of CECs and predicting their behavior has been a daunting⁶ challenge. Evaluation⁷ is costly⁸, tedious and time-consuming. Further, as the new study emphasizes, laboratory modeling of chemical behavior, including rates of environmental breakdown⁹ and potential for bioaccumulation often deviate¹⁰（脱离） significantly from real-world scenarios¹¹.

 

Conventional chemical screening evaluates the persistence¹², bioaccumulation and potential toxicity¹³ of various chemicals. The method however suffers from two shortcomings: the production rates of chemicals in current use are not incorporated into analysis and the detailed¹⁴ behavior of these chemicals in real-world biological systems -- including the human body -- is not assessed.

 

In the current study, a repository of samples from U.S. wastewater treatment plants, created and maintained by Halden at ASU's Biodesign Institute was used to conveniently identify CECs, as well as evaluate their potential for bioaccumulation and their ability to withstand degradation¹⁵ processes. The working hypothesis proposes that such treatment plants may act as reliable gauges¹⁶ for monitoring chemical prevalence and bioaccumulation potential relevant to human society and the environment.

 

Specifically, chemicals managing to survive primary and secondary treatment in municipal sewage systems display notable resistance to aerobic¹⁷（需氧的） and anaerobic¹⁸ digestion¹⁹ processes and are therefore more likely to stubbornly persist in the environment upon their release.

 

As Halden notes, post-treatment sludge provides a sink for water-avoiding (hydrophobic) organic compounds. Such sludge is often applied²⁰ to land, where the persisting hydrophobic chemicals (including polychlorinated biphenyls [PCBs], briominated flame retardants [BFRs] and various pharmaceutical²¹ and personal care products including antimicrobial agents) can accumulate in considerable quantity.

 

The analysis identified a total of 123 chemicals in biosolids. Of these, 17 brominated chemicals were detected in U.S. biosolids for the first time. The most abundant chemicals were surfactants, which occur commonly in detergents²²（洗涤剂）, emulsifiers（乳化剂）, foaming²³ agents and dispersants.

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