Grantee Research Project Results
Final Report: Phototransformation of Contaminants at the Sediment-Water Interface
EPA Grant Number: R830394Title: Phototransformation of Contaminants at the Sediment-Water Interface
Investigators: Tratnyek, Paul G.
Institution: Oregon Health & Sciences University
EPA Project Officer: Packard, Benjamin H
Project Period: March 1, 2002 through February 28, 2004 (Extended to September 30, 2006)
Project Amount: $198,226
RFA: Futures Research in Natural Sciences (2001) RFA Text | Recipients Lists
Research Category: Futures , Ecological Indicators/Assessment/Restoration , Land and Waste Management , Hazardous Waste/Remediation
Objective:
The major hypothesis underlying this study was that the lack of information on photochemistry at the sediment-water interface (SWI) is a significant contributor to uncertainty in risk assessments involving contaminated sediments. To reduce this uncertainty, we proposed to: (1) survey a range of contaminant-sediment combinations using a variety of protocols to identify the types of situations where photoeffects at the SWI are most significant; (2) develop improved and alternative methods for studying SWI; (3) apply a range of chemical and physical probes to obtain a detailed understanding of the controlling processes; and (4) perform a preliminary assessment of the overall importance of these effects relative to other environmental fate processes and use this understanding to anticipate future problems and/or opportunities for improved management practice.
Summary/Accomplishments (Outputs/Outcomes):
Initially, we tested three representative contaminants (atrazine, pentachlorophenol, and disulfoton) for photoeffects on contaminant concentrations at SWIs formed with fresh-water sediments in laboratory microcosms. Disulfoton gave the strongest evidence for photolysis that was influenced by the SWI, so we used it to probe differences between sediment types (three were tested, but differences were small) and effects of added sensitizers and traps (which supported the hypothesis that the effect of disulfoton photolysis at the SWI is due to enhanced production of singlet oxygen, presumably due to natural organic matter at the interface). Photooxidation of disulfoton at the SWI was partially reversed overnight, presumably due to microbial reduction in the absence of light.
The potential coupling between photooxidative and reductive (dark) transformation pathways at the SWI led us to study another probe compound, 2-chloroacetophenone (2-CAP). The fate of 2-CAP in reducing sediments is known from our previous work, and here we showed that 2-CAP also undergoes facile photolysis to yield products that are distinct from those formed by reduction. Irradiation of 2-CAP at the SWI gave slower disappearance of 2-CAP and a mixture of oxidation and reduction products. We were not able to obtain mass balance, however, and it is not clear if this system gave any “intrinsic” SWI photoeffects that might impact contaminant fate more broadly.
In response to the need for better methods to investigate processes at the SWI, especially those driven by sunlight, we attempted to measure vertical profiles of nitric oxide (NO) across the SWI during illumination. Using a microelectrode for NO, we did observe vertical gradients, but it was not clear that this response was stratification of NO and not spurious phenomena—like direct photo-response of the electrode.
Conclusions:
Currently, assessments of the risk from contaminated sediments do not take into account the effect of sunlight at the SWI, even though there is a strong possibility that photoeffects could alter the fate of contaminants or their effects on benthic organisms. This project was the first extensive evaluation of what photochemical processes need to be considered, what types of contaminants provide the greatest risk, and what types of sedimentary environments are most likely to be impacted. We found evidence that some contaminants—specifically some organophosphate pesticides—undergo a dynamic transformation process at the sunlit SWI. We believe this avenue of study has great promise, but further work will be needed to characterize the full range of potential effects of this type.
Supplemental Keywords:
contaminated sediments, wetlands, organics, pesticides, exposure, risk assessment, toxics, oxidants, phototoxicity, UV effects, environmental chemistry, environmental monitoring, geochemical modeling,, RFA, Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Contaminated Sediments, Monitoring/Modeling, Environmental Monitoring, Ecology and Ecosystems, UV effects, geochemical modeling, phototoxicityRelevant Websites:
http://www.ogi.edu/project/swi/ Exit
http://www.stccmop.org Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.