Incorporating Unique Exposure Pathways of the Diné People into a Community-Based Probabilistic Risk Assessment Following the Gold King Mine Spill

On August 5th 2015, the Gold King Mine Spill released 3 million gallons of acid mine drainage-containing arsenic (As) and lead (Pb) into a tributary of the San Juan River, which flows through the Navajo Nation. The Diné (Navajo) rely on this River and use it for a variety of purposes lending to unique exposure pathways. We administered questionnaires in three Navajo communities in collaboration with the Navajo Nation Community Health Representatives to obtain frequency and duration data on 42 activities. These activities were utilized to conduct a community-based probabilistic risk assessment from exposure to As and Pb: 1) before the Spill, 2) during peak of the Spill, and 3) one year after the Spill. To estimate exposure to As and Pb before the Spill, we utilized historical surface water (n=32) and sediment data (n=20) obtained from the USGS. Estimation of exposure to As during peak Spill incorporated As and Pb surface water (n= 92) and sediment (n=75) concentrations obtained from U.S. EPA publically available data. To estimate exposure to As and Pb one year after the Spill, we collected surface water (n=101) and sediment samples (n=127) in these three Navajo communities within one year after the Spill. Surface water concentrations of As and Pb were significantly different between periods (p-value <0.0001), with concentrations highest during the peak of the Spill, followed by pre-Spill and post-Spill levels. Sediment concentrations were significantly different (p-value <0.0001), but with concentrations highest before the Spill, followed by peak-Spill, and post-Spill. The risk assessment for arsenic and lead through these unique water/sediment pathways indicate both potential chronic and carcinogenic risks to the local Diné community. This research provides the first documentation of unique exposure pathways of the Diné people and raise the need to understand and document unique exposure pathways of indigenous communities with subsistence and land-based livelihoods.