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UBC Theses and Dissertations

Investigation of molecular markers to identify sources of nitrate contamination in groundwater Mitchell-Parsotan, Margaret Ann

Abstract

Molecular markers were investigated as potential tools for differentiating between the sources of elevated nitrate-N in the Hopington AB Aquifer. Residential use (septic systems) and agriculture (livestock) have been identified as key land use activities, which overlay the Hopington AB Aquifer, and thus possible contributors of nitrate-N to the groundwater. Harmful levels of nitrate-N concentrations above the drinking water limit of 10 mg/L have been detected in the well of a private resident (14 mg/L) and spring water (17 mg/L), which were located on the aquifer. DAS 1 (a diaminostilbene) and DSBP (a distyrylbiphenyl) are fluorescent whitening agents (FWAs), which in the Fraser Valley are present in 3 out of 4 popular laundry detergents, and have been detected in domestic wastewater at concentrations of 7.84 and 2.36 μg/L respectively; thus they are suitable markers for septic systems in Langley. Sulfamethazine, which is an antimicrobial approved solely for veterinary use in Canada, is widely used in the livestock industry. Good maximum recoveries for DAS 1 (60%), DSBP (125%) and sulfamethazine (125%), coupled with low method detection limits ranging from of 0.01 — 0.04 μg/L implied that solid phase extraction (SPE) and high-performance liquid chromatography (HPLC) with an ultra violet (UV) detector were adequate for the determination of the molecular markers. The detection of DAS 1 (3.14 μg/L) and DSBP (0.05 μg/L) in the final effluent at a BNR (biological nutrient removal) pilot plant suggested that the FWAs were not completely removed by wastewater treatment processes including primary clarification, biological (aerobic and anaerobic), and membrane filtration; thus, once released, these FWAs may persists in the environment. In this study, DAS 1 (0.01 — 0.13 μg/L) was detected in 4 wells belonging to private residences, which were located on the Hopington Aquifer. DAS 1 (0.05 μg/L) and DSBP (0.02 μg/L) were also detected in spring water, which were located down gradient of septic systems. These results suggested that septic tank systems have contributed to the overall nitrate in the aquifers. The non-detection of the FWAs at the two control sites (Hopington C and Abbottsford) confirmed the specificity of DAS 1 and DSBP in relation to source. Overall, the FWAs exhibited fairly conservative behaviours due to their abilities to be source specific and persistent in the environment. As a result, they are useful tools for the identification of septic system sources of contamination in the environment. Sulfamethazine was not detected in any of the Hopington AB wells; however, further research is needed in order to determine if this antimicrobial was an appropriate molecular marker for livestock activities.

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