Health risk analysis of human exposures to soil amended with sewage sludge contaminated with polychlorinated dibenzodioxins and dibenzofurans.

The risk of cancer to humans exposed to soil treated with wastewater/sewage treatment plant sludge, known to be contaminated with small amounts of polychlorinated dibenzodioxins and dibenzofurans (PCDDs and PCDFs), was evaluated. The particulate-bound PCDDs and PCDFs are found in trace amounts in the effluent from ground water pumping (dewatering) at an abandoned wood preservation facility. The water, which was sent to a water recovery plant, underwent primary and secondary treatment prior to discharge. The residual sludge was added to agricultural soil as a conditioner. The present analysis treats the extreme case of sludge applied near the home of a target individual, a lifetime resident, who is also a farm worker in the area of the application. The successive stages of infancy, childhood and adulthood are treated separately to assess the contributions of typical age-specific indoor and outdoor activities on exposure rates. Five toxicity rating schemes using so-called TCDD equivalents, and two unit risk slopes are applied to the chemical profile in sludge to determine the cancer potency of the soil contaminants. These risk estimates range from 1 X 10-8 to 3 X 10-7.