Occurrence of iodinated X-ray contrast media in domestic effluents and their fate during indirect potable reuse

This study investigated the occurrence of pharmaceuticals, emphasizing triiodinated benzene derivatives used as X-ray contrast media, in domestic effluents and their fate during subsequent groundwater recharge. Organic iodine measurements were used as a surrogate for triiodinated benzene derivatives. Seven wastewater treatment facilities in Texas, Arizona and California were studied and organic iodine concentrations at these facilities varied between 5 and 40 μg iodine/L. The highest concentrations were observed on weekdays reflecting the common practice of employing X-ray examinations between Monday and Friday. Organic iodine compounds in secondary treated effluents were not removed by advanced wastewater treatment using ozone. However, organic iodine was efficiently removed by reverse osmosis membrane treatment. Based on laboratory biodegradation experiments and field studies negligible removal occurred under aerobic redox conditions while anoxic conditions led to partial removal of organic iodine. However, a concentration range of 8-15 μg iodine/L was observed in groundwater recharge systems after travel times of 8 to 10 years. Beside appropriate redox conditions, bioavailable organic carbon seems to be a key factor for organic iodine biodegradation in the environment. No environmental risk is expected from the parent compounds of triiodinated contrast media, however, toxicological effects associated with the metabolites are unknown.