Use of biodegradable dissolved organic carbon (BDOC) to assess the potential for transformation of wastewater-derived contaminants in surface waters.

Wastewater-derived contaminants (WWDCs), such as steroid hormones, pharmaceuticals and personal care products, have been detected in surface waters at concentrations that pose potential risks to aquatic ecosystems. To assess the factors controlling biotransformation of these compounds in effluent-dominated surface waters (i.e., surface waters containing a high proportion of wastewater effluent), microcosm experiments were conducted with 10 pharmaceuticals and five steroids typically detected in wastewater effluent. Some of the compounds underwent rapid biotransformation under all conditions (estrone, 17beta-estradiol, progesterone, testosterone and triclosan), while carbamazepine was always resistant to biotransformation. For the remaining compounds, the rate of biotransformation was related to the amount and type of biodegradable dissolved organic carbon (BDOC). The rates of biotransformation of these WWDCs increased as the initial concentration of wastewater BDOC increased, indicating a relationship between microbial activity and biotransformation rate. Furthermore, BDOC derived from aquatic plants resulted in a better ability to remove certain recalcitrant compounds (gemfibrozil and sulfamethoxazole) as compared to that derived from wastewater effluent. These observations indicate that for each source of BDOC, it may be possible to use BDOC for predicting the rate of biotransformation of WWDCs in surface waters.