Timeline: 2006 – 2008
Client: California Department of Transportation (Caltrans)
Study Locations: Laboratory studies at the Department for Civil and Environmental Engineering, UC Davis
Role: PM/Lead Scientist
Background:
Under Section 303(d) of the 1972 Clean Water Act, states, territories, and authorized tribes are required to develop a list of water quality limited segments. These waters on the list do not meet water quality standards, even after point sources of pollution have installed the minimum required levels of pollution control technology. The California Water Board currently has many waters on this 303(d) list, and regional water boards are responsible for establishing and implementing TMDLs in these watersheds.
On the 2002 303(d) list are 258 water bodies with biological contaminants (i.e., pathogens, high coliforms, bacterial indicators, or Enterococci). Of these, most sites are listed with point/nonpoint sources or source unknown, but a total of 55 have runoff/storm water listed as a definitive source. Several other studies (Ackerman and Weisberg 2003, Boehm et al. 2002; Noble et al. 2003) have shown correlations between rainfall events and widespread pollution of fecal indicator bacteria at southern California coasts. While roadways contribute the largest proportion of impervious surfaces, one might assume their runoff is highly loaded with pathogens. However, there is no knowledge about the distribution of pathogenic pollution to different surfaces. Tools have to be found to quantify pathogens and land-use specific fecal loads that can produce reliable results independent of specific sample matrices.
The purpose of this Task Order was to complete a set of methods and protocols for environmental monitoring of stormwater. The objective was to be able to measure real pathogen loads in highway runoff and identify sources of microbial contamination. The microbial source tracking approach is based on the occurrence of bacterial cells of the order Bacteroidales that are indicative of feces originating from specific host organisms broadly attributable to human, domestic pet, cattle, or horse waste. Bacteroidales are among the key organisms currently targeted by the U.S. EPA for microbial source tracking.
Knowledge about decay rates of quantified targets is a key component. In situ experiments were conducted to assess the persistence of genetic markers in freshwater and seawater and the influence of light. This information will significantly increase the utility of monitoring data. Additionally, a conditional probability approach was used to develop a quantitative statistical model to provide confidence limits for reported microbial source tracking data.
Another specific goal of the task order includes the development of a suitable surrogate that can be added to stormwater samples and used to determine filtration efficiencies for the quantitative detection of protozoan pathogens like Cryptosporidium and Toxoplasma. Particularly, the presence of pathogens that are infective in low numbers accentuates the importance of reliable and sensitive test methods. For the optimization of the detection of pathogens and bacterial markers by qPCR suitable methods have to be found that ensure efficient nucleic acid extraction and quantification/detection. Knowledge about the affinity of pathogens to solids in the context of ultrafiltration is also missing. Therefore, the sorption of viruses and the question of whether pathogens and bacterial markers are lost due to association with solids is examined in this study. PCR inhibitors prevalent in natural samples such as humic acids can significantly interfere with the quantification of targets and even lead to false non-detects. Finally, methods to treat inhibitors have been reviewed and developed. Furthermore, the previously developed methods and processes were optimized in regard to sensitivity, recovery, and quantitation.
Publication:
Schriewer A., Wehlmann A. and Wuertz S. (2011). Improving qPCR Efficiency in Environmental Samples by Selective Removal of Humic Acids with DAX-8. Journal of Microbiological Methods. 85 (1), 16-21.
Report:
Schriewer, A., Bae, S., Rizvi, A., Sirikanchana, K., Wang, D. and Wuertz, S. (2009). Completion of environmental toolkit for fecal source tracking and pathogen analysis in stormwater. Report prepared for the Environmental Division of California Department of Transportation. Report #: CTSW-RT-09-168-23.2.