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A characterization of pesticides in secondary treated effluent (STE) and a screening health risk assessment were conducted to evaluate potential health impacts of recycled water for potable reuse. Samples of STE were examined pre- and post-reverse osmosis (RO) treatment in two plants. Risk quotients (RQ) were estimated by expressing the maximum and median concentration as a function of the health value. Of 128 pesticides analyzed, 11 were detected in STE. Trifluralin was detected in 86.5% of the STE samples followed by metolachlor (67.6%), 2,4-D (50%), and propiconazole (42.5%). Metolachlor was the only pesticide detected post-RO in one sample (0.08 μg/L, limit of reporting = 0.05 μg/L). RQ(max) were all below health values in the STE with the exception of thiophanate methyl (RQ max = 2.4). RO was able to reduce the concentration of all pesticides below LOR. Median removal efficiency for RO ranged from 67.1% (atrazine) to 98.8% (2,4-D). The results indicate that, despite the detection of pesticides in STE, the impact on indirect potable reuse is negligible due to the low concentrations in STE and their subsequent removal during RO treatment. Implementation of risk management strategies to optimize safety and recommendations for a monitoring program are also discussed. [ABSTRACT FROM AUTHOR]

The city of Perth in Western Australia is facing a future of compromized water supplies. In recent years, this urban region has been experiencing rapid population growth, coupled with drying climate, which has exacerbated water shortages. As part of the government strategy to secure water sustainability and to address an agenda focused on all elements of the water cycle, a target of 20% reuse of treated wastewater by 2012 was established. This includes a feasibility review of managed aquifer recharge for indirect potable reuse. A characterization of contaminants in wastewater after treatment and an assessment of the health implications are necessary to reassure both regulators and the public. To date, the commonly used approach involves a comparison of measured contaminant concentrations with the established drinking-water standards or other toxicological guidelines for the protection of human health. However, guidelines and standards have not been established for many contaminants in recycled water (unregulated chemicals). This article presents a three-tiered approach for the preliminary health risk assessment of chemicals in order to determine key contaminants that need to be monitored and managed. The proposed benchmark values for the calculation of risk quotients are health based, systematically defined, scientifically defensible, easy to apply, and clear to interpret. The proposed methodology is based on the derivation of health-based levels for unregulated contaminants with toxicity information and a "threshold of toxicological concern" for unregulated contaminants without toxicity data. The application of this approach will help policymakers set guidelines regarding unregulated chemicals in recycled water. [ABSTRACT FROM AUTHOR]