Identification of chemicals of potential concern (COPECs) in anthropogenic wetlands of the Colorado River delta

An early step in an Ecological Risk Assessment (ERA) process is the screening of chemicals to identify those that constitute a potential risk by comparing concentrations to levels that are believed to be nonhazardous or “benchmarks”. In the present study we analyzed concentrations of metals and metalloids (mercury, arsenic, selenium, and copper) as well as organochlorine pesticides in samples of water, sediment, and fish from the Cienega de Santa Clara wetland, Rio Hardy wetland, and the Upper Gulf of California-estuary. These wetlands are located in northwestern Mexico in the Colorado River delta. All contaminants analyzed were retained as Chemicals of Potential Ecological Concern (COPECs). Mercury was identified as a priority COPEC due to its potential negative effects in freshwater biota, benthic invertebrates and fish eating birds in all three study areas. Copper posed a potential high risk to Rio Hardy aquatic biota. Arsenic represented a risk to aquatic plants and to benthic invertebrates of the three areas with special concern at the Upper Gulf of California-estuary. Selenium was found at levels that could cause a slight (5.6%) reduction in avian reproductive success at the Cienega de Santa Clara and Rio Hardy, similar to the effects found at the Salton Sea. For organochlorine pesticides, DDT represented a potential high risk for aquatic biota at the Cienega de Santa Clara and Rio Hardy, DDD posed a risk for fish eating birds at the Cienega de Santa Clara, and DDE represented a high risk for fish eating birds at the Rio Hardy. In addition to these contaminants, other published studies in the area have identified chromium, lead, boron, PCBs, organophosphorous pesticides and contaminants of emergent concern (CECs) as toxic or potentially toxic for aquatic biota, benthic invertebrates, and wildlife. We recommend to follow-up with an ERA process where the actual effects of COPECs in species and plants of concern (i.e. endangered, rare, keystone species) are evaluated.