Assessment of water quality and benthic macroinvertebrate community at a wastewater receiving constructed wetland in El Paso, Texas

Background/Question/Methods

Pharmaceuticals and personal care products (PPCPs) are a class of emerging environmental contaminants that are widely used in human and veterinary medicines. Main routes of PPCPs to the environment are via improper disposal of prescribed medications, agricultural run-off, and  wastewater.  Rio Bosque Wetlands Park (El Paso, TX) receives treated effluent from an adjacent wastewater treatment plant.  Using wastewater to fill the wetland is a concern due to the unknown effects of un-remediated compounds, specifically, PPCPs to benthic macroinvertebrates.  Chironomids are frequently the most abundant group of macroinvertebrates in freshwater aquatic systems as well as key bioindicators of water quality.  The responses of chironomids to PPCPs have not been widely studied.  The effects of selected PPCPs on chironomids inhabiting Rio Bosque will be determined.  Samples from three sites were collected from September 2009 to January 2011.  General water chemistry parameters were monitored and additional samples were retained for detection of 13 highly used PPCPs.  Sediment samples were collected to analyze benthic macroinvertebrate diversity, PPCPs, and to obtain live chironomids for exposure studies to four selected PPCPs.  Water quality samples were measured with a YSI^® MPS 556 and Palintest^® kits.  PPCPs samples were analyzed with an HPLC-MS/MS. 

Results/Conclusions

Water quality results showed that as the wetland developed, from September 2009 – December 2009, inorganic nitrogen increased throughout the wetland.  However, in January 2010, all levels of these compounds were elevated:  ammonia (7.2 – 14.8 mg/L NO₃-N), nitrite (5.8 to 7.74 mg/L NO₂-N), and nitrate (9-13 mg/L NO₃-N).  On most occasions nitrate levels ranged from 5.1-22 mg/L NO_3^- N, and exceeded the IBWC’s criteria of 1.95 mg/L NO_3^-N.  All other water chemistry parameters tested were similar throughout the wetland.  Benthic macroinvertebrate abundance was initially low with only three taxa: Chironomidae (0-7 individuals), Coleoptera (2 individuals), and Nematoda (0-12 individuals).  Thus far the dominant taxon is Chironomidae at all sites ranging from 0 to 4,359 individuals from September-October 2009 samples.  Chironomids were exposed to caffeine in a 48-hour LC₅₀ exposure which resulted in the LC₅₀ concentration being 1.7 g/L of caffeine. Future work will include determining concentrations of PPCPs from sampling sites, acute exposure studies on three additional selected PPCPs:  triclosan (an antibacterial/antifungal agent); sulfamethazine (an antibacterial); and acetominaphen (an analgesic/antipyretic) to determine the acute toxicity of each compound.  Results from this study will aid in our understanding of the impacts of these compounds on aquatic systems.