Level and extent of mercury contamination in Oregon, USA, lotic fish

Abstract

We conducted a probability survey of 154 Oregon, USA, stream and river sites to assess the spatial extent of mercury (Hg) contamination in fish tissue. Samples consisted of whole-fish analyses of both small (<120 mm) and large (>120 mm) fish at each site, when both were present. Overall, Hg levels (microgram/g) in small fish (mean = 0.031; standard deviation [SD] = 0.029), large piscivores (mean = 0.284; SD = 0.175), and large invertivores (mean = 0.055; SD = 0.047) were found within fairly narrow ranges; always above detection (0.0025 microgram/g) and almost always below 0.4 microgram/g. Given the great ecoregion diversity across Oregon, the narrow range in fish tissue Hg levels suggests that atmospheric transport is an important vehicle for Hg distribution. In small fish, Hg levels were almost always low and showed little meaningful difference among fish taxa. In large fish, Hg levels were significantly related to fish length. Piscivores (pikeminnow and bass) had significantly higher Hg levels, and the slope of their Hg level/length relationship was much steeper than for invertivores. Salmonids, the most commonly occurring fish taxon in Oregon, exceeded 0.1 microgram Hg/g (deemed protective for fish-eating mammals) in an inferred 15% of stream lengths where they occurred. Pikeminnows and bass were found at fewer sites, but they exceeded 0.1 microgram Hg/g in an inferred 96 and 70%, respectively, of stream lengths where they occurred.

Evaluation of Potentially Nonlethal Sampling Methods for Monitoring Mercury Concentrations in Smallmouth Bass (Micropterus dolomieu)

“…Future studies would require a moisture determination for each sample or would have to rely on moisture values from other studies. Alternatively, the samples could be analyzed wet by CA-AAS (e.g., Peterson et al 2005), but precision is generally lower due to among-sample moisture differences and the samples would have to be analyzed soon after collection to avoid moisture loss; Peterson et al (2002) Blood Hg, µg/mL demonstrated that plug samples can be stored for up to 100 days. Negative attributes of the biopsy punch include the generation of solid waste and the relatively large, visible wound it leaves, which would presumably be sealed prior to releasing the fish (Baker et al 2004).…”

“…It is also not appropriate for threatened or endangered species. Studies conducted elsewhere have demonstrated the utility of muscle biopsy sampling as an alternative to sampling fillets or whole fish for Hg monitoring (Baker et al 2004;Cizdziel et al 2002aCizdziel et al , 2003Peterson et al 2002Peterson et al , 2005Uthe 1971) and selenium (Hamilton et al 2004;Waddell and May 1995) and for obtaining samples for genetic analyses (Crawford et al 1977;Leitner and Isely 1994). The analysis of scales (Lake et al 2006) and caudal fin tissue (Gremillion et al 2005) have also been evaluated for Hg.…”

Critical perspectives on mercury toxicity reference values for protection of fish

“…The Beckvar et al [8] TRV of 0.2 mg/kg falls at the high end of present-day background concentrations of mercury in larger fish ( Table 5), but fish tissue mercury concentrations [129] comparable to this TRV apparently can occur naturally under conditions that favor mercury methylation, such as in dystrophic lakes or in watersheds with abundant forest and wetland cover [32,35,102]. Taken together with the uncertainties in the data underlying this TRV (see section Review of fish tissue TRVs), it would appear that the Beckvar et al [8] TRV is lower than necessary for protection of adult and early life stages of fish.…”

A Biointegrity Index (IBI) for Coldwater Streams of Western Oregon and Washington

“…Historical disturbances in the 19th century (overfishing, hatcheries, logging, channelization, estuary restructuring, and fire) have influenced the biological integrity of streams, but often are not evident in current habitat and land use descriptors (Benner and Sedell 1997;Harding et al 1998;Connolly and Hall 1999). Reduced numbers of returning adult salmon and the resultant lower nutrient inputs (Gresh et al 2000) are not detected by our human disturbance measures, nor are chronic levels of atmospheric contaminants like mercury (Peterson et al 2002). All of these factors may mean that our reference sites were degraded somewhat from historical or natural conditions.…”