What are sewage sludges?
Sewage sludges, or “biosolids” are the semi-solid material that remains after sewage treatment facilities process wastewater from homes, businesses, medical facilities, and industry. In some communities, runoff from roads, lawns and fields is also sent through the facility. Legislation mandating treatment requirements for wastewater (the Clean Water Act), necessarily resulted in double the amount of sludge produced, and changing sludge management practices (shifting away from ocean dumping, landfills and incineration) include the viewing of sludges as a resource. Organic matter and nutrients make sludges a potentially valuable addition to soils, and sludges are, in fact, widely used as a soil amendment. However, there are no requirements in the US to test for or remediate organic pollutants in sewage sludges and sludges contain a variety of these contaminants that conventional treatment does not eliminate. These contaminants present a range of possible exposure scenarios for wildlife and people. The Cornell faculty in these two interviews address in their work various aspects of the identification, degradation activity, and approaches to management and bioremediation of chemicals in sludges.
(Sludge information adapted from Cornell Waste Management Fact Sheet, “The Production of Biosolids/Sludge” )
Vol. 12 Issue 4, Fall 2007
Your lab addresses several challenges with regard to contaminants in the environment, from the detection of chemicals in diverse settings – such as sewage sludges – to developing approaches to degrading harmful compounds.
Anthony Hay: Yes, we are interested in some of the contaminants that are in sludge, many of which originate in the home. Most of the wastewater treatment plants that are around today were designed with the idea of meeting wastewater treatment rules that target industrial pollutants. Even today the monitoring and the reporting that is done only has requirements for some industrial pollutants. There are no requirements for chemicals from personal care products, pharmaceutical compounds, or antibiotics. There is a disconnect between some of these newer concerns and what is monitored.
At what stage of a given pollutant’s “journey” are the biodegradation processes that you are studying relevant -- during wastewater treatment, sludge processing or “digestion,” or in the broader environment?
AH: Biodegradation is relevant to all aspects. We are finding that the wastewater plant itself is not well adept at either removing or degrading these compounds, and that’s in part because it is optimized for a different suite of compounds. We are interested in knowing if and how biodegradation is happening in the environment. What types of genes would be present in an environment where these things are getting dumped, and is the biological capacity there to degrade these pollutants? By understanding the biology, we can then look at the various environments – whether it is the sewage treatment plant, or the lake that is receiving the treated water, or the soil that is getting the sludge amended to it. We think that by understanding the basic biology we can address questions in all of those realms.
How does a typical municipality treat its wastewater?
AH: The typical municipality treats to remove primary indicators like biochemical oxygen demand, fecal coliform bacteria, nitrogen, and phosphorous; those are the main components that they are concerned about and on which the EPA mandates they report. Depending on the size of the facility, they also have to do a yearly assessment of certain industrial pollutants. As we talk a little bit about in the review article on which Ellen Harrison is the lead author (reference at end of article), the types of compounds targeted by the required analyses do not include any of the pharmaceuticals and personal care products that are now being seen at high levels in sludges.
Have you heard of any municipalities that have addressed these compounds?
AH: Some municipalities try to institute various tertiary treatments; those might be ultraviolet treatment, or ozonation, for example. These are usually effective technologies for attacking these kinds of compounds, or organic pollutants in general. Constructed wetlands are another type of tertiary treatment for wastewater. In Ithaca they recently built up a biological phosphorous removal plant, and there is some evidence that you get additional organics removal with this treatment. Concern about phosphorous is pushing a lot of the wastewater treatment changes. But again, these changes are not driven by pharmaceuticals, personal care products, or any other endocrine disrupting compounds; these are simply not on the radar screen yet for wastewater treatment.
There are questions in the scientific literature about how low concentrations need to be for us to stop being concerned about them. Just because a compound is present, doesn’t mean it’s harmful. And, at this point, everything is everywhere. The question is: are those pollutants present in concentrations sufficient to cause biological harm? The problem is that we don’t always know the endpoint of concern: is it, for example, estrogen response, is it enzyme inhibition, or is it some other endpoint we don’t know about? An example is tributyl tin, an anti-fouling biocide that is polluting coastal waters. New research is showing that it functions as an environmental “obesogen.” That is, it promotes the accumulation of fat and adipocytes. This emphasizes the point that there are endpoints that we don’t fully understand. We do have to know the dose-response relationship and that not all doses are important, but the other side is that we have to know the range of endpoints that need to be measured. The more we study, the more we realize that there are additional sensitive endpoints that we have not known about in the past.
Your work focuses on the ability of microorganisms to degrade pollutants. What is an example of that process?
AH: Yes, we like to say, “bugs on drugs.” For example, there are microorganisms that grow on ibuprofen. Ibuprofen is the third most consumed drug in the world. Wastewater treatment plants remove about 90% of it, but given the volume that is being consumed, that is still a lot being given out to the environment. No one knew previously how ibuprofen was degraded. Sometimes biodegradation is incomplete, and can result in things that are more toxic than what you started out with. So understanding the biological fate is very important for being able to predict the potential for toxicity of compounds. In the case of ibuprofen we were able to show that it was degraded to non-toxic intermediates.
This contrasts with some commonly-used detergents, like alkylphenol ethoxylates, which start out relatively nontoxic, but when they are degraded, the spectrum of activity – the biological endpoints that they target – changes, as well as how long they persist in the environment. The alkylphenols change from something that just has a detergent effect to something that binds with a hormone receptor and can cause a cascade of activities to take place in the body. The concentrations being reported are below levels of concern for most human populations but there are a lot of ecologically sensitive organisms. Fish, for example, have been shown to undergo changes in sex ratios, resulting in fewer males. The question is, what is the long-term effect on populations? We don’t really know.
Aquatic effects are what has driven any regulatory activity on these compounds in this country, correct?
AH: Yes. Definitely.
Can you elaborate on this process of the spectrum of biological activity changing toward increased toxicity with biodegradation? Where in the process is it happening?
AH: We call it activation, and it happens all along the way. Alkylphenol ethoxylates can be degraded when oxygen is present or when it is absent. As soon as you have conditions that allow microbes to grow, like the inside of your drain, they can begin to metabolize the ingredients in household products.
Compounds of specific interest in your lab include the alkylphenols and triclosan. How do you determine which chemicals to examine? How much of the load of estrogen potency of chemicals in sewage sludge is accounted for by the alkylphenols?
AH: We have worked on both detecting these chemicals in sludges, and on their biodegradation. Originally we just wanted to determine whether they present in our sludges. We had heard of them being reported elsewhere, and didn’t suspect that ours would be any different or worse. But we found that alkylphenol in sludges from the four communities in the Northeast that we studied had levels that were five times higher than other places that had been studied. The ranges we found of 1500-2000 mg/kg, which is .1 - .2% by weight, is quite a lot for any organic pollutant. We then wanted to know if that was a one-time event, or true through all the seasons and over a number of years. So we studied four treatment plants, monitoring them seasonally. We found that there were fairly constant levels present. When we portrayed that alkylphenol quantity in terms of what it meant to an estrogen receptor, we found that there was about 15-20 times more alkylphenol-related estrogenicity than has been reported for dairy manures, which are thought to have a high level of estrogenicity due to the lactating cows.
With respect to how much of the total of estrogen-like burden in sludge is accounted for by the alkylphenols, we really don’t have a good sense; the level of overall estrogen potency of sewage sludge is a good question.
The four sites you worked on had exclusively domestic input to the wastewater, except one with an industrial mix, correct?
AH: We looked at alkylphenols in Syracuse, Cortland, Ithaca, and Cayuga Heights (a suburb of Ithaca) wastewater treatment plants, and expected Syracuse to have the highest, but that was not always the case, especially when we looked at the estrogen equivalency. Cayuga Heights actually had a lot more octylphenol, which is the alkylphenol with the most estrogenic potency.
So when we looked at total predicted estrogenic potency, it was highest for Cayuga Heights. There are differences in the way the treatment plants are operated. Cayuga Heights has a trickling filter. The others have aeration basins that use a different technology. Other researchers have looked at alkylphenol level in sludges that were produced by different types of processes and have not found consistent links. What really needs to be done is to determine what’s coming in versus what’s coming out, because the processes do differ so greatly.
Can you speak about the two other chemicals that were included in this work?
AH: Abigail Weiss Porter did this work. She also measured sludge levels of triclosan, a widely used biocide, present in almost all the antibacterial hand soaps that you can buy, as well as in a lot of deodorants, toothpastes, many products. It’s not even all that effective. In fact, one of the students working with me, Lauren Junker, looked at antimicrobial effects of plastics with triclosan and found no antimicrobial effect. Yet these things are marketed to what we called the “microbophobic” public. Triclosan was present in all of the sludges in quite high concentrations, in concentrations that would inhibit microbial activity in laboratory media. When they are in a complex mixture like a sludge, however, they are not likely to be as bioavailable, so they are not going to be as potent. We are seeing triclosan increasingly in environmental samples. We are finding triclosan in fish, and it is found in high concentrations in breast milk. Triclosan is an inhibitor of the enzymes that are involved in cleaning out other pollutants from our body; part of phase-2 metabolism.
Abigail also looked at HHCB or Galaxolide, a synthetic polycyclic musk found in perfumes and deodorants, which has endocrine disrupting activities. It is a compound that is very persistent, and doesn’t disappear in soils. The levels of HHCB were very constant in our study; we saw it in every sample and the concentrations did not vary very much.
I think we should all be concerned with what we are putting down the drain. I do product searches every year, and I am seeing some voluntary phase out of some of these compounds. Without US regulatory activity on these, it becomes “good business practice,” especially with regard to exporting products to Europe, where, under the REACH program, (http://ec.europa.eu/environment/chemicals/reach/reach_intro.htm), regulation of these chemicals is much more rigorous than the US.
You and Abigail Weiss Porter have a new paper coming out addressing the identification of a gene involved in the biodegradation of octylphenol (reference below). What does it mean to have identified this gene? What is the next step?
AH: Abigail’s research showed that the organism that we had isolated from the Ithaca wastewater treatment plant was able to grow on alkyphenol and it did that using a flavin monooxygenase. This protein was able to activate oxygen and get that oxygen incorporated into the alkylphenol, making a metabolite that broke off the chain. It went from alkylphenol to a phenol derivative and alkyl group.
That phenol derivative was actually very toxic to the cell and she had a hard time getting the cells to keep wanting to make the enzyme because that phenol derivative, hydroquinone, was toxic to the cells. This goes back to that question of activation. Sometimes pollutants aren’t easily degraded in the environment because the degradation products are toxic to the cells. One of the questions we would like to ask about the environmental fate or the relevance of this is: are these things being degraded to intermediates that prevent further degradation, therefore killing the very organisms that are trying to degrade them. That has implications for persistence in the environment and might help to explain why these things are so long lived. We are learning from a number of different studies that in microorganisms in nutrient poor environments, like a lake, may not able to withstand the metabolism of toxic compounds as easily as in laboratory settings. Especially if a toxic by-product is being made. Dealing with these toxic insults limits the cells ability to multiply, and therefore could limit any biodegradation that might take place in the environment. We would like to build on Abigail’s work by trying to understand if these same pathways are occurring in the environment, and if the levels of degradation are self-limiting because of toxic intermediates.
Can you comment on related work going on at Cornell and the history of Cornell’s contribution to these research questions about biodegradation and their applications?
AH: Marty Alexander is the “godfather” of biodegradation. As a soil microbiologist here in Crop and Soil Sciences, he really helped pave the way for understanding what affects the biological fate of pollutants in the environment. He is extremely well respected in the field, and made significant contributions to understanding the factors that limit biodegradation.
I can’t begin to list all the work that is being done here at Cornell, but more specific examples of ongoing research include that by James Gossett in the School of Civil and Environmental Engineering and Stephen Zinder in the Microbiology department, who discovered the bacterium that’s able to grow on chlorinated ethanes like DCE and vinyl chloride, which are important groundwater pollutants. This process which they discovered has been shown to be working in aquifers and sediment environments all over the world, and, together with Ruth Richardson (also in the School of Civil and Environmental Engineering), they have developed tools to monitor that process. They have done a great job in focusing on a specific problem and bringing to bear biological and engineering expertise that is now resulting in cleaner environments in local areas all over the US and the world.
Beth Ahner in Biological and Environmental Engineering looks at phytochelins and other components of the cell that mobilize heavy metals like lead and cadmium. Christopher Ober and Emmanuel Giannelis in Materials Science and Engineering are looking for replacement compounds for things like tributyl tin; they are looking at polymers that can be used as anti-fouling coatings on ship hulls so toxic chemicals are not needed. Ann Lemley in the Department of Fiber Science & Apparel Design has a very focused program looking at the degradation of pesticides at the point source, and developing a technology that can one day be an inexpensive way to destroy leftover pesticides.
There is a group of people at Cornell beginning to look at nanomaterials in the environment. Len Lion and Claude Cohen have developed nanomaterials to remove pollutants from solids; others are looking at the toxic effects of nanomaterials to see if they act differently than the bulk chemicals we are used to studying. There are far too many examples to list them all but this gives you a flavor for some of the things that are going on at Cornell.
Let’s close by returning to the problem of contaminants going down the drain and, in many communities, resulting in sludges or “biosolids” that contain toxic compounds. What can communities do?
AH: Although tertiary treatments like ultraviolet treatment or ozonation can dramatically reduce a lot of these trace organics that are making it through traditional wastewater treatment plants, these technologies are expensive and most communities have little incentive to install them. In the absence of legislation it really is the consumer that is going to drive changes right now; we can each make the choice to change the products we buy and think more carefully about what we put down the drain.
Would you start by telling us about the use of sludge as a soil amendment?
Ellen Harrison: The management of sludges is a significant component of the cost associated with wastewater treatment and disposal. Applying sludge as a soil amendment is often the cheapest option. The majority of sewage sludge produced in the US is being applied to agricultural, forest, mine or park lands. Some is being sold or given away to private citizens. Before being applied to land, sludges must be treated to reduce pathogen concentrations, but no treatment is required that addresses the chemical contaminants. And, no labeling is required, so citizens may be unknowingly purchasing sludge products. Some products are even using the term “organic” on their labels.
You, Dr. Hay, and your research team produced a major gap-filling work in recent years: a thorough review of the existing peer-reviewed and governmental reports on the presence of organic chemicals in sewage sludge. First of all, can you explain the possible implications of the presence of contaminants in sewage sludge?
EH: Current sludge regulations address only a handful of contaminants and we have little information on thousands of chemicals that go down the drain. Our concern is that we are spreading such a complex mixture of chemicals – from pharmaceuticals and personal care products to PCBs – across the landscape where we eat, work and play. Given our lack of knowledge about what is in sludges and of the risks associated with even those chemicals we have identified, the impacts on human and ecological health are impossible to assess.
With our ability to measure very small concentrations, an important question is whether the amounts of chemicals detected in sludges have environmental or health significance. To address that question, we used a measure suggested by the National Academy of Sciences, National Research Council, in their assessment of sludge. We compared the measured concentration of sludge contaminants to US EPA Soil Screening Levels (SSLs). We found that most of the chemicals were found in some sludges at concentrations exceeding these SSLs, indicating that they are present at levels high enough to warrant concern.
What did you find in the available reports, and, equally important, what data were not available?
EH: Finding relevant data was not easy. Since testing is not required, we had to rely on research conducted by academic and governmental institutions. Out of the many thousands of chemicals that are probably in sludges, we were able to find data on only 516. Many of the research papers did not contain information on the type of treatment processes or the characteristics of the industries contributing sewage, so we could not draw general conclusions about the sources and control of various chemicals. The lack of standard analytic methods also makes it difficult to compare results of different studies, since large differences in measured concentrations can result from using different laboratory methods.
What classes of chemicals found strike you as especially important for additional attention, and why?
EH: A number of endocrine disrupting chemicals (EDCs) are found in relatively high concentrations in sewage sludges, including brominated flame retardants, and nonylphenols, as well as pharmaceutical hormones. The ecological impact of EDCs is of great concern. Our survey also found that short-chained chlorinated aliphatic compounds (trichloroethylene for example) and monocyclic hydrocarbons (benzene and toluene, for example) were reported at concentrations in sludges that routinely exceeded the SSLs. Almost no data were found for nitrosamines which is surprising given their toxicity and the fact that they are likely to be formed during sewage treatment. Unfortunately, a current effort at the US EPA to examine additional contaminants in sludges is not addressing these contaminants.
Within the Cornell Waste Management Institute, which you direct, sewage sludge is one of several areas of focus. What are your objectives in this area of the Institute?
EH: Our role at the Cornell Waste Management Institute is to promote and conduct applied research and outreach to help people, from governmental policy makers to farmers and gardeners, make decisions based on sound science. To ensure our independence, we have a policy not to take funding from anyone with a financial stake in the outcome of our work. We post all our work on our much-used web site (http://cwmi.css.cornell.edu/) so that people can have free access to the work we do.
As with all environmental health issues, a lot of different players need to come to the table in order to make progress. Who are the necessary players for cleaning up sewage sludge?
EH: Elimination or reduction in use, as well as upstream controls at the point of industrial discharge into the sewer, have reduced concentrations of some contaminants. However, we send such a mixture of chemicals down the drain, that I do not think that it is realistic to clean up sewage sludges to a point that I would be comfortable with their use as a soil amendment. Separating the wastewater from homes from that coming out of industrial and other non-domestic sources could help reduce the burden of chemicals in sewage sludges, although residential sewage also contains pharmaceuticals and personal care products. In my view, we need to develop other ways to manage sludges. There are new energy recovery options that may provide a better option.
Is there a role that the public can play?
EH: Many of the contaminants of concern in sludges are “bad actors” wherever they are found. Working to ban such chemicals from use will limit our exposure. California, for example, has banned the use of the more toxic brominated flame retardant, which is a good step.
People should find out where the sludge from local treatment plants is being disposed. They should also be aware of whether sludges are being used on the grounds of the schools and parks where their children play. When they obtain compost or soil amendments for use on their yards, they should find out whether they contain sewage sludge. And of course, they should try to use products that don’t contain toxic chemicals and should not flush unwanted chemicals or pharmaceuticals down the drain.
Harrison, E.Z., Oakes, S.R., Hysell, M., and Hay, A. (2006). Organic Chemicals in Sewage Sludge. Science of the Total Environment 367, 481-497.
Porter, A.W., and Hay, A.G. (2007). Identification of opdA, a gene Involved in Biodegredation of the Endocrine Disruptor Octylphenol. Applied and Environmental Microbiology, 73. Doi: 10.1128/AEM.01478-07