Tuesday, November 14, 2006 - 8:25 AM

Do PBDEs and Alkylphenol Ethoxylate Derivatives in Land-Applied Sludges Pose a Risk?.

Robert C. Hale, Virginia Institute of Marine Science, Dept of Environmental and Aquatic Animal Health, Chesapeake Bay Hall, S310, Gloucester Point, VA 23062

Farming is under increasing pressure due to escalating fuel and fertilizer costs.  Accordingly, land application of biosolids, as an inexpensive soil amendment, is attractive.  However, the potential risks of this practice deserve additional scrutiny; especially in light of reported illnesses and as viable farmland dwindles due to encroaching development. Biosolids arise from the co-mingling of run-off, residential and industrial wastewaters.  Thus they contain a plethora of unspecified synthetic chemicals, degradates and biologically-derived agents.  Calculation of attendant application risks is less straightforward than assumed in the EPA risk assessment underlying the Part 503 regulations.  To illustrate, that assessment did not consider many chemicals present in sludge, e.g. two high production volume chemicals: polybrominated diphenyl ethers (PBDEs) and nonylphenols (NPs).  PBDEs, flame retardant polymer additives, were originally believed to possess limited migration potential and bioavailability.  This was later refuted as high burdens in wildlife, humans and biosolids were reported.  Recently the U.S. manufacture of 2 of the 3 PBDE formulations voluntarily ceased production after years of debate.  NP polyethoxylates (NPEOs) are widely used nonionic detergents.  Their environmental risk and persistence were initially portrayed as low.  However, it was subsequently discovered that NPEOs can be degraded to NPs, e.g. during wastewater treatment.   NPs are more persistent and bioaccumulative and exhibit greater acute toxicity and endocrine disrupting potential than their precursors.  Interestingly, NPs have found use as spermicides and are believed to be responsible for reductions in smolting success in wild populations of Canadian Atlantic salmon at low ppb levels.  Burdens in biosolids vary as a function of source and stabilization, but may surpass a part per thousand.  The discussion suggests that dogma as to the safety of two chemicals detected in biosolids have proven wrong over time.  Similarly, the proclamation that land application of biosolids is “safe”, merits continuing scientific evaluation.