Fate and Transport of Trace Organic Compounds in Various Ecosystems

Abstract

For perhaps eleven months of the year, surface water flow in the Santa Cruz River consists entirely of wastewater effluent from the Roger Road Wastewater Treatment Plant (RRWTP) and the Ina Road Water Pollution Control Facility (IRWPCF). Like other conventional plants that treat primarily domestic wastewater, effluents from the RRWTP and IRWPCF contain numerous trace organic contaminants--an unintended consequence of our reliance on water to carry waste from points of generation to central treatment facilities. The fates of these compounds in the environment are not entirely clear since the instruments necessary to measure process-dependent changes in concentrations at levels relevant to environmental health are just now coming into widespread use. Chemical fate during planned or incidental infiltration and transport to points of recovery is therefore relevant to the quality of delivered water, as water and contaminants are transported in surface waters and unintentionally reused. Interventions that reduce human and environmental exposures to contaminants present in this water, including natural processes, are thus important to protect human health. Here, it is hypothesized that there is a reasonably continuous discharge of trace organics from wastewater treatment effluents to the Santa River. Because the river is effluent dependent, and travel times can be determined from gauging station flows, some measure of fate and transport of trace organics in the surface water can be obtained. The relative levels of trace contaminants in wastewater treatment plant effluent and downstream waters will provide compound specific attenuations due to dilution with native ground water, sorption on sediments, biodegradation, etc. If destructive mechanisms can be distinguished from dilution, the resultant analysis will be of general interest--an indication of the combination of travel distance and time of travel that is necessary to protect the public when recovered water is eligible for unrestricted potable use without additional treatment. Primary Objectives. *To measure the time-dependent changes in trace organic composition of Santa Cruz River water. *To determine if correlations between known quantities such as biodegradation can be correlated to compound attenuation or persistence during travel. *To apply conclusions from the Tucson data set to other location where dilution and time of travel are also contributing factors; Austin TX and Boston MA. In Tucson, the data suggests that relatively biodegradable compounds are removed by natural processes on a time scale of hours. In areas where dilution and time of travel differ from the Tucson area; such as the Boston area, greater transport distances and times of travel in the Charles River (Boston area) resulted in natural attenuation of most compounds measured, suggesting that even biochemically persistent compounds such as carbamazepine, TCEP and sulfamethoxazole are attenuated to a degree during in-stream transport over periods of days to weeks. The mechanism(s) for these removals is not clear, and the effects of dilution from tributaries are uncertain despite efforts to account for those flows. The limited data from a dry period in a short stream reach in the Little Colorado River (Austin), which was also analyzed, generally support this picture. With one or two exceptions (e.g. DEET), there is limited evidence of compound attenuation between the two proximate monitoring points. Overall, the data indicate that natural mechanisms can be counted on to biochemically degrade or physiochemically transform many of the trace contaminants that are added to surface streams in municipal wastewater effluents. Time scales for compound disappearance range from hours (for relatively biodegradable compounds) to weeks. Although none of the contaminants reported on here is now subject to US federal drinking water regulations, the human health effects of long-term chronic exposure to multiple trace organic contaminants at sub-ppb levels remain uncertain. Environmental impacts are generally acknowledged. Cost effective risk management due to trace organic exposure may eventually include reliance on natural attenuation during in-stream transport to downstream points of reuse.