Fate of Endocrine Disruptors Following Long-Term Land Application of Class B Biosolids and Risks to Public Health

In a field study, the fate of estrogenic activity, nonylphenol, and PBDEs in soil was determined following 20 years of land application of Class B biosolids. The study was conducted under highly controlled conditions at a university research site in southern Arizona, USA. Four replicates of plots containing biosolids land applied at two rates, and control plots were utilized in this study.Following twenty years of annual biosolid application, four sets of soil cores were collected from each treatment (one core sample from each replicated plot using a soil auger core 7.5cm in diameter to a depth of 150 cm in 30 cm intervals) in December 2005, nine months after the final land application in March 2005. Soil samples were taken from each of the treatment plots across a transect line down the length of the plot to determine the soil chemical properties as a function of depth. Measurements of selected endocrine disruptors (EDCs) within soil were used to assess their long term fate and their potential for adverse human health effects via risk assessment.Estrogenic activity, nonylphenol and polybrominated diphenyl ethers (PBDEs) were all assayed following accelerated solvent extraction of soil samples. Estrogenic activity was determined via a yeast estrogen screen bioassay. Nonylphenol was measured via HPLC. PBDEs were assayed via GC-ECD analysis of the hexane extracts. Risk assessments, where appropriate, were made based on intake of compounds via inhalation, dermal sorption or ingestion. Data show that low levels of nonylphenol were detected in the soil samples. However, nonylphenol has a much lower estrogenic response than estrogen steroidal hormones, and assuming a potency ratio of 8,500:1 (nonylphenol:ethinylestradiol) a nonylphenol concentration of 1271 ng per g soil would be needed to elicit on estrogenic response. The highest measured nonylphenol concentration was 1,253 ng per g soil, consistent with the nondetection of estrogenic activity in any soil sample. However, significant PBDE concentrations were detected, primarily in the surface 30 cm depth sample. Surface accumulation of PBDEs occurs due to their hydrophobic nature which results in sorption to colloids. The maximum amount of PBDE detected was 80ng/g soil as congener BDE- 209. A risk evaluation of PBDEs based on “Hazard Indices” indicated that the health risk to humans of PBDEs was negligible even when all three routes of exposure were considered. Based on data for these selected endocrine disruptors found in soil following long term land application of Class B biosolids, it would appear they do not pose a significant risk to human health.