TOXICITY OF HEAVY METALS IN WATERS AND SEDIMENTS FROM MINE-IMPACTED SITES IN PRINCE WILLIAM SOUND, ALASKA AS MEASURED BY INHIBITION OF BETA-GALACTOSIDASE SYNTHESIS IN TEST E. COLI

Toxicity is a complex interplay of chemical species, mobility, and bioavailability of the element or compound under consideration. In the past, toxicity assays involved measuring the short-term (acute) response of indicator macroinvertebrate or fish species under laboratory conditions, but assessment of a large number of samples was infeasible due to the time and costs involved. Bioassays based on microorganisms such as protozoa, microalgae, or bacteria (“microbioassays”) fill the need for rapid sample screening. Even with these advances, heavy metal toxicity in environmental matricies has been difficult to assess directly, because most assays are sensitive to toxic metals and toxic organic compounds alike.

The use of two commercially available, heavy metal-specific microbioassay kits (MetPAD and MetPLATE) to measure metal toxicity in waters and sediments from Prince William Sound, Alaska, will be discussed in this presentation. Weathered mine wastes from Cu mines active in the early 20th century are found in the intertidal zone along several fjords and islands of the Sound. High levels of As, Fe, Cu, Pb, Zn, Tl, and Hg have been measured in waters and sediments from these sites, and could have an adverse impact on near shore marine ecosystems. All assays were run with negative and positive controls, and involved adding genetically modified E. coli to waters or sediment slurries, reacting for a specified period, adding enzyme substrate, and measuring color production (inversely proportional to sample toxicity). Initally, MetPAD kits were used with only semi-quantitative results, but a more sensitive and quantitative assessment can be achieved using the MetPLATE kits, in which color development is assayed spectrophotometrically. We found toxicity to vary between and within sites, with more toxic water samples collected from the site with substantial acid mine drainage (AMD) versus the two sites that did not have AMD. However, metal-free, acidic water is also toxic to the bacteria, a fact that must be considered. Seawater and “background” samples collected from pristine streams near the mine sites showed low or no toxicity.