Some characteristics of limestone aquifers, in contrast to porous media, make them particularly susceptible to contamination. Sinking streams and sinkholes provide a rapid route for unfiltered contaminants from the land surface to the underlying aquifer. This characteristic, along with swift groundwater flow in conduits that have been widened by mineral dissolution (karst aquifers) and difficulty characterizing and monitoring the highly heterogeneous karst subsurface, contributes to an elevated risk for degradation of water quality. The reliance on groundwater for drinking supplies in karst regions creates potential for public health effects.
The nonprofit Karst Waters Institute held an interdisciplinary conference to explore knowledge gaps between the science of contaminant transport in karst aquifers and our understanding of exposure pathways and health outcomes. Sponsorship was provided by the National Institute of Environmental Health Sciences, Puerto Rico Testsite for Exploring Contamination Threats (PROTECT), the National Science Foundation, and the Edwards Aquifer Authority of central Texas.
Seventy experts from seven countries attended. They specialized in karst hydrogeology, contaminant geochemistry, microbiology, public health sciences, and environmental law and regulation. Attendees grappled with identifying conceptual and practical obstacles while they learned of new tools, findings, and promising perspectives for protecting human health. Sessions highlighted emerging tools for investigating contaminant transport, for quantifying exposure concentrations, and for demonstrating linkages to human health outcomes.
Numerous presenters demonstrated that karst is particularly prone to groundwater contamination that may undermine human health, with several studies documenting higher concentrations of bacteria and protozoa in karst than in porous media aquifers. In addition, molecular tools for tracing and identifying potential pathogens in groundwater revealed large numbers of viruses derived from humans as well as from wildlife and livestock.
Most conclusions about human health outcomes are based on interpretation of public health data that are collected independently of information on the factors that exacerbate groundwater contamination. Only one study presented at the meeting had sufficient data to link the timing of disease outbreak to the occurrence of stormflow that mobilized contaminant migration into groundwater supplies used for drinking.
More commonly, scientists rely on simplistic geographic associations between groundwater contamination and disease outbreak. Given the place-based nature of hydrogeological studies, we recommend that spatially distributed health data be reported to help reveal the intersection of water quality and human health. Participants discussed ways that general regulations for water quality protection may not be appropriate in karst regions, where contaminants are transmitted rapidly from the land surface to the water table, and they debated creative nonregulatory approaches to manage land use as another means of protecting water supplies.
The significant time lag between the occurrence of water supply contamination, particularly by chemical agents, and the subsequent health outcomes in the population represents a fundamental misalignment of environmental and human data. Meeting participants discussed how newly applied methods in time series analysis hold promise for resolving the mismatch.
Because the perspective of each investigator determines what is measured in a given study, it is critically important to develop comprehensive observations by conducting interdisciplinary studies and by sharing data. Participants at this conference developed an expanded appreciation for the need to collect diverse types of data during their investigations. The consensus was that new insights and connections would emerge from increased communication. An edited volume of research papers from the meeting is under contract for publication.
—Janet S. Herman, Department of Environmental Sciences, University of Virginia, Charlottesville; email: [email protected]; Dorothy J. Vesper, Department of Geology and Geography, West Virginia University, Morgantown; and Ellen K. Herman, Department of Geology, Bucknell University, Lewisburg, Pa.