Pepper, I.L., Quanrud, D.M. Takizawa, K., Gerba, C., The University of Arizona(free)
We evaluated the fate of two emerging contaminants: endocrine disruptors that are known to be in Class B biosolids, and prions which have been shown to occur in the environment, and could potentially end up in biosolids. Soils that had received annual applications of Class B biosolids for 20 years were analysed for the presence of PBDEs and nonylphenol. Data show that PBDEs which are hydrophobic, sorbed to colloids in the surface soil, and were resistant to degradation. PBDE soil concentrations were low and risk assessments showed that risks to human health were negligible. Nonylphenol concentrations were low indicating that they had been rapidly degraded within the soil. A recent publication evaluating the fate of prions in the environment stated that prions were capable of surviving mesophilic wastewater treatment. However, the assay used in that study did not evaluate the infectivity of the prions. We utilized a new assay for the detection of infectious prions and re-evaluated the fate of prions within biosolids. Prions added to biosolids and incubated at 35oC showed 1.5 log inactivation in 15 days compared to 2.5 log inactivation in 10 days when incubated at 60oC. These data indicate that prions do not survive wastewater treatment.
Keywords: endocrine disruptors, infectious prions
Emerging contaminants currently cause great concern nationally and include both chemical and biological entities. Chemical emerging contaminants include pharmaceuticals and personal care products that function as endocrine disruptors. Biological emerging contaminants include not only newly discovered pathogens, but also infectious proteins known as prions.
Endocrine disrupting compounds (EDCs) are chemicals that interfere with endocrine glands or their hormones. Among the EDCs present in wastewater, estrogenic compounds have received the most attention due to their well documented detrimental effects in exposed fish. Estrogenic activity in wastewater effluent and in biosolids is due to presence of residual amounts of steroidal hormones, nonionic surfactant metabolites (including nonylphenol), and other types of compounds. During anaerobic sludge digestion, alkylphenols are broken down to nonylphenol and other lower chain alkylphenol polyethoxylates that have greater estrogenic potency than the parent nonionic surfactants. Nonylphenol concentration in biosolids can reach levels of parts per thousand and thus contribute a significant component of the total estrogenicity in biosolids. Polybrominated diphenyl ethers (PBDEs) are additive flame retardants used in everyday household items including carpets and cushions. PBDEs are a known class of EDCs that are typically present at ppm levels in municipal biosolids produced in the USA, but data on the fate of PBDEs following land application are limited. PBDEs consist of two benzene rings with an ether linkage. Substitution with up to 10 bromine atoms yields 209 congeners with physical characteristics that differ primarily based on degree of bromination. In general, hydrophobicity increases and bioaccumulation/toxicity decrease with bromine addition. The magnitude of PBDE manufacture and use of these compounds in clothing and home furnishings guarantees their presence in municipal wastewater and sludges produced from wastewater treatment. Environmental exposure to PBDEs related to wastewater reuse, and use of biosolids as a soil amendment remains a concern.