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Sludge as new sentinel for human health risks

January 16, 2014

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 (chemicals of emerging concern), which may pose risks to both human and environmental health. 

Arjun Venkatesan, a recent doctorate, and Rolf Halden, professor and director of the Center for Environmental Security at Arizona State University’s Biodesign Institute, have carried out meticulous tracking of many of these chemicals.  portrait of Rolf Halden Download Full Image

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 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. 

The study shows a strong overlap 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 assessment of human exposure and bioaccumulation of potentially hazardous 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 daunting challenge. Evaluation is costly, tedious and time-consuming. Further, as the new study emphasizes, laboratory modeling of chemical behavior, including rates of environmental breakdown and potential for bioaccumulation, often deviate significantly from real-world scenarios. 

Conventional chemical screening evaluates the persistence, bioaccumulation and potential toxicity 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 detailed 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 degradation processes. The working hypothesis proposes that such treatment plants may act as reliable gauges 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 aerobic and anaerobic digestion 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 applied to land, where the persisting hydrophobic chemicals (including polychlorinated biphenyls, PCBs, briominated flame retardants, BFRs and various pharmaceutical 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 detergents, emulsifiers, foaming agents and dispersants. 

After surfactants, pharmaceutical and personal care products were most abundantly detected, followed by BFRs, which commonly occur in plastics, textiles, electronics and household flame-retardants. BFRs often persist and bioaccumulate in the environment, and, under proper conditions, are also capable of transforming into other hazardous chemicals, including brominated dioxins and furans. The study notes that the pathways by which BFRs enter wastewater treatment facilities remain speculative, requiring further investigation

The surfactant and antimicrobial chemicals identified fall into the category of high production volume compounds, produced in annual quantities of over 450,000 kg (1 million pounds). The study notes that the abundance of some chemicals is traceable to specific societal events – for example, the 2001 anthrax scare, which significantly boosted production and consumption of the antibiotic ciprofloxacin. Antibiotic accumulation in the environment is of particular concern, due to a tendency to cause heightened drug resistance in microbial pathogens.  

The study reveals that 91 percent of the 11 most abundant compounds detected in biosolid samples are high production volume chemicals, reinforcing the strong link between the occurrence of hydrophobic chemicals in sludge and their production volume.  

Hydrophobic compounds occurring in the range of parts per trillion are generally of low environmental occurrence or experience significant biodegradability, or both. On the other hand, those chemicals occurring in parts per million quantities are of potential concern, owing to low biodegradability, high usage and the tendency to accumulate in biosolids due to their hydrophobic nature.                                          

When results of the current study were matched against a comprehensive exposure assessment of environmental chemicals conducted by the Center for Disease Control and Prevention, it was observed that roughly 70 percent of chemicals detected in biosolids were also detected in humans. 

Chemical abundance in biosolids appears to be a reliable indicator of current rates of chemical usage, resistance to biodegradation and potential for bioaccumulation. Further, by using biosolids as a pre-screening step, researchers may reduce the thousands of potentially hazardous CEC chemicals in circulation to a manageable number of priority substances most in need of further evaluation. Such a list of chemicals could then be scrutinized with respect to their absorption, distribution, metabolism and excretion, as well as their potential harmfulness to humans and ecosystems.

“With over 85,000 chemicals in daily use in the U.S., it is a daunting task to pinpoint those that need more monitoring, regulation or replacement with safer alternatives,” Halden says. “It turns out that we can use existing infrastructure – our wastewater treatment plants – to take the chemical pulse of the nation, determine chemical inventories and zero in on risky chemicals prone to harm people, prosperity and the planet.” 

Richard Harth

Science writer, Biodesign Institute at ASU


Evolutionary medicine expert joins ASU faculty

January 16, 2014

Editor's Note: The Center of Evolution, Medicine and Public Health kicks off its inaugural lecture and symposium series Jan. 17. For the schedule, click here.

Randolph M. Nesse, one of the world’s preeminent researchers and teachers in the field of evolutionary medicine, joins the Arizona State University faculty this semester. Dr. Randolph M. Nesse, M.D. Download Full Image

Nesse is settling into his academic home in the School of Life Sciences, in the College of Liberal Arts and Sciences, where he is foundation professor and founding director of a new Center for Evolution, Medicine and Public Health. The center will be part of the Biodesign Institute research network.

Before joining ASU, Nesse was professor of psychiatry and psychology at the University of Michigan, where he also was research professor at the Institute of Social Research and director of the university’s Evolution and Human Adaptation Program.

“ASU was attractive to me because the university has great faculty working in this area – in the School of Life Sciences, Biodesign with its superb Center for Evolutionary Medicine and Bioinformatics led by Sudhir Kumar, the School of Human Evolution and Social change, and in departments like psychology – as well as a strong partnership with the Mayo Clinic,” Nesse said.

“The university is innovative, forward-thinking and is perfectly positioned to be the preeminent place in the world for changing how we think about human health. It is my vision that people from all over the world who are interested in evolutionary medicine will come here to study.”

Nesse said it was at an academic meeting with ASU professor Robert Page, now university provost, and Manfred Laudbichler at which the path to ASU was initially set.

“Randy’s dream was to teach evolutionary medicine to doctors, to change the way they treat patients, and we were fascinated by what he was doing,” said Page. “We were building these programs with Mayo and we thought ASU would be the perfect fit for Randy’s vision.

“We need to look at different ways to advance the research enterprise at ASU. So we are looking for opportunities to make big leaps, to grab that emerging wave before it has crested. Evolutionary medicine is poised to be huge, and we want to be the place to put it on the map. Randy will help make that happen.”

According to Nesse, his early work on the origins of biological aging and the neuroendocrinology of anxiety soon led to a fascination with evolution. He collaborated with George Williams on several early works in Darwinian medicine, including “The Dawn of Darwinian Medicine” and the book "Why We Get Sick: The New Science of Darwinian Medicine."

Evolutionary medicine, or Darwinian medicine, is the application of modern evolutionary theory to understanding health and disease. The goal of evolutionary medicine is to understand why people get sick, not simply how they get sick. Modern medical research and practice has focused on the molecular and physiological mechanisms underlying health and disease, while evolutionary medicine focuses on the question of why evolution has shaped mechanisms that leave us susceptible to disease.

Nesse’s primary current research focus is on how natural selection shaped the capacity for high and low moods and the mechanisms that regulate mood and anxiety. His work emphasizes the utility of negative emotions in certain situations, and how a signal detection analysis (the “smoke detector principle”) can help to explain why anxiety and other aversive emotions are, like fever and pain, expressed so often when they do not seem necessary.

He is particularly interested in the utility of low mood in disengaging effort from unreachable goals, and whether inability to give up large unattainable goals might help to explain the prevalence of depression. This proves valuable in his work as a practicing physician specializing in psychiatry, a field that is just beginning to recognize the utility of the well-developed evolutionary principles that are the foundation for the study of animal behavior.

Nesse has taken on the mission of publicizing the diverse additional contributions evolution could make to medicine if doctors learned evolutionary biology as a basic medical science, and the ways this can improve human health. This has involved extensive writing, lecturing and helping to organize the growing evolution and medicine community. 

Nesse is also president of the Evolution, Medicine and Public Health Foundation, which sponsors two publications, The Evolution & Medicine Review, which he edits, and Evolution, Medicine, & Public Health, an Oxford Press open-access journal edited by Stephen Stearns, with a team of 89 associate editors, that publishes original, rigorous applications of evolutionary biology to problems in medicine and public health. As Nesse says, “The field is entering a phase of exponential growth that will be much faster and better, thanks to ASU.” 

Nesse holds a bachelor of arts from Carleton College and a doctor of medicine from the University of Michigan Medical School.

Sharon Keeler

associate director, Ira A. Fulton Schools of Engineering