September 2015

What about trace chemicals and metals in biosolids?

"We've discussed this often, so I'm not certain what new "perspective" you desire.  Yes, all of those constituents could theoretically end up in sewage sludge to some extent. For all but the currently regulated pollutants (As, Cd, Cu, Hg, Mo, Ni, Pb, Se, and Zn), there are data that show that they are either present in such low concentrations / not a biological concern in the chemical forms as not to pose a hazard (and, therefore, not require monitoring) or are no longer produced and not accumulating to any extent (and, therefore, not require monitoring). 

"There are research studies on some of the PPCPs [pharmaceuticals & personal care products] that seem to indicate little cause for concern, but some scientists continue to question the use of biosolids due to a "what if" factor. Not every chemical compound requires testing because there are many fewer chemical functional groups under which these compounds can be grouped. Therefore, if we understand how a certain chemical group imparts toxicity, carcinogenicity, or endocrine disruption, we can infer how the larger numbers of these products having the same chemistry would react. Scientists can then address the concerns exhibited by compounds posing the greatest risk due to a combination of concentration, bioactivity, and presence in the environment from biosolids use.

"The greatest unknown today is the potential for synergistic, additive, or multiplicative effects. These have not been demonstrated, but are routinely identified as concerns. 

"The pathways for many of these products from source (e.g., flame retardants in carpets, computers, chair cushions) to human is much more direct from the products that incorporate these chemicals than from land where biosolids are applied. 

"As more wastewater facilities move to Class A or bettertreated Class B products, the minimal risk of pathogens previously observed has been reduced more.  The greatest evidence for the lack of risk from land application is the lack of evidence of people getting sick where the biosolids have been used for many years. 

–Greg Evanylo, PhD, Professor, College of Agricultural & Life Sciences, Virginia Tech, Blacksburg, VA


Some "handouts... raise concerns in those who don't know the science of biosolids, or even general agricultural/environmental science.  Greg... noted that everything on Earth contains trace levels of all 92 natural elements. Soils contain certain levels mostly because the elements are either insoluble over millennia, or added in small amounts in fertilizers to maintain soil fertility. The USGS 2013 report summarizes their analysis of thousands of soil samples collected across the USA.... I find this provides some perspective if one is seeking science rather than fear. Soil elements are mostly so insoluble that they are not taken into plants even at the low parts per billion level.

"[We actually measure some elements in plant samples to estimate the soil contamination of crop samples from windblown dust, or soil contact during harvest -- elements such as titanium, zirconium, yttrium, chromium and most of the rest of the rare earth elements. Even with soils geologically rich in these elements, plants do not accumulate the element, but dust contamination can be estimated by analysis of several of the elements compared to levels in the fine particles of soil.]

"In testing uptake by plants, some add fresh spikes of soluble metal salts, but research has clearly shown results from such testing are severely flawed and have no bearing on uptake of elements equilibrated and weathered in soils. Or those applied in stabilized biosolids. Huge errors have been reported in research purported to represent biosolids but using spiked element additions.

"Some elements do reach edible plant tissues grown on biosolids amended soils, and those that are common in biosolids were subjected to risk assessment and development of the 503 regulation. There is simply no information which shows that after long term use of biosolids as a fertilizer that foods grown on the amended soil would comprise risk to highly exposed individuals based on the home garden model (which gives much more potential for exposure than the general agricultural market model). 

"The same principles have been found to apply to organics/xenobiotics. Yes, many of the chemicals used by society can be found in biosolids at least at measurable levels now that we have extremely sensitive methods to measure these compounds. In most situations, the use of consumer products in our homes provides a massively higher exposure to humans than could be possible from biosolids use in agriculture or even in garden fertilizer/soil conditioner products.

"Soluble compounds move more to the effluent and lipophilic compounds that persist thru aerobic and anaerobic treatment at the POTW can reach the biosolids. One of the important lessons of risk from such compounds came from study of PCBs. Recall in the 1970s science discovered PCB contamination, and common commercial use without attention to industrial pretreatment caused some biosolids to be quite high in PCBs. Study of pure chemical PCBs spiked to soils showed some uptake to the peel of carrots, and the lesser chlorinated PCBs were even volatilized from soil to shoots of plants. But when biosolids borne PCBs were examined, even the transfer to peel of carrot was highly significantly lower than occurred from spiked soils. Eating soil by livestock was the only way for detectable levels of biosolids-applied PCBs to reach livestock tissues.

"Risk from other xenobiotics in biosolids need to test potential uptake from soils amended with appropriate levels of the xenobiotic in biosolids, preferably not 1000-times higher than is commonly found in US biosolids as has been used in some "scare" experiments. Based on this view of appropriate experimental tests, none of the xenobiotics on the list you sent comprises risk to humans, and likely not even a risk to soil organisms, because the compounds are sufficiently insoluble that they are bound strongly by the organic matter in soil and added with biosolids. 

"Regarding the pathogens, Greg's response is the simple reality. EPA and VA regulations require management which prevents transfer of pathogens in Class B products to humans or the environment at levels of concern, and the increasing production of Class A products is further protection of all of the environment. Class A is better in the sense that it requires less management supervision to prevent risks and POTWs are increasingly moving toward Class A products to win public acceptance. But that is not needed to achieve the low level of risk required by US-EPA and states which is achieved by the Class B use constraints. 

"Scientists who have been involved in biosolids constituent risk assessment and development of regulations recognize the flaws in experiment design that have allowed some to publish research that is purported to show a risk from nanoparticles or xenobiotics or trace elements in biosolids. Bad science is simply bad science. Only proper experiment design can test whether a constituent of biosolids can be transferred from the biosolids to plants or animals. Rates of application relevant to biosolids, in the matrix of biosolids products ready for land application, has to be the standard for testing these potential risks.

"Occurrence is not evidence of transfer to foods. And study of spiked soils or nutrient solutions provides no evidence relevant to real world risks from constituents of biosolids. Please continue to stand on the strong science which supports beneficial use of biosolids in agriculture." 

– Rufus Chaney, PhD, Senior Research Agronomist, USDA-ARS-CSGCL, Beltsville, MD