Mercury Concentrations in Stream Fish Throughout 12 Western States in the USA Alan Herlihy and Robert Hughes Dept. of Fisheries & Wildlife, Oregon State University Spencer Peterson and John Van Sickle EPA NHEERL Corvallis, OR

Questions What is the extent of mercury (Hg) contamination in fish tissue across all Western U.S. streams and rivers? What are the factors related to mercury levels in fish at this scale?

Environmental Monitoring and Assessment Program (EMAP) Western U.S. Pilot Survey Sample sites were selected using the systematic, randomized EMAP sampling design from all perennial western U.S. streams/rivers –Additional hand-picked reference sites Samples selected off of the digitized version of the 1:100,000 scale USGS maps Inferences to the entire stream network can be made from probability survey data using site inclusion probabilities

Field Methods Fish sampled by electrofishing Streams: backpack shocker on 40 channel width long sample reach Rivers: raft mounted shocker on 100 channel width reach Associated measurements of water chemistry, physical habitat, and watershed characteristics

Tissue Samples Collect a big and small fish sample at each site if sufficient numbers available Big Fish: ≥ 120 mm total length –Up to 3 individuals of 3 different species of varying size, individuals analyzed separately Small Fish: Adults < 120 mm –Single composite sample ( g) Samples kept on ice, shipped overnight to laboratory and then frozen until analysis.

Hg Laboratory Analysis Whole body analysis (µg Hg/g wet weight) Fish ground up in blender (bass-o-matic) Subsampled, frozen with no further sample preparation Subsamples thawed, rehomogenized, ≈0.25 g analyzed by Combustion AAS (Milestone MDA80 direct Hg analyzer) Subsamples analyzed in duplicate, –repeat if > 5% difference Method Detection Limit = µg Hg/g wet wt.

Most Common Species Analyzed Big Fish (2,707 fish, 626 sites) Non-Piscivores (85%) –Rainbow, Brown, Brook, Cutthroat Trout –White, Largescale Sucker –Mountain Whitefish, Carp Piscivores (15%) –Smallmouth Bass –Northern Pikeminnow –Walleye, Northern Pike Small Fish (386 samples) –Mottled Sculpin –Common Shiner –Redside Shiner –Fathead Minnow –Creek Chub –Speckled Dace –Longnose Dace

Three Aggregate Level III Omernik Ecoregions used in Analysis

Mercury – Fish Length Relationship for Individual Big Fish

Factors to Consider Fixed Factors –Ecoregion (Mountains, Xeric, Plains) –Site Disturbance Class (Low, Medium, High) –Trophic Group (Piscivore, Non-Piscivore) Covariates –Fish Age (Fish length) Analysis of Covariance using individual big fish

Big Fish ANCOVA Results EffectF-valueP - valuedf Fish Length330< Trophic Group120< Ecoregion Site Disturbance Trophic x Ecoregion11<.00012

Non-Piscivores Piscivores Fish Tissue Mercury in Trophic x Disturbance Class

Fish Tissue Mercury in Ecoregion x Trophic Classes Non-Piscivores Piscivores Non-Piscivores Piscivores

Correlation between Hg and environmental variables in Big Fish after partialing out the effect of fish length Piscivores (n=358) Most strongly correlated with –ANC (r = -0.57) –Conductivity (r = -0.56) –Watershed Slope (r = 0.52) –Precipitation (r = 0.51) –% Forested Watershed (r = 0.5) –Sulfate (r = -0.5) Non-Piscivores (n=1,964) –No variables correlated with r > 0.3

Various Fish Tissue Mercury Criteria Values Human Health – 0.5, 0.6, 1.0 µg/g – 0.35 µg/g (Oregon Health Div., 1997) – 0.30 µg/g (EPA, 2001) – 0.10 µg/g (Faroe Island Study, 1998) Wildlife protection values - Lazorchak et al – 0.10 µg/g (Otter) – 0.07 µg/g (Mink) – 0.03 µg/g (Kingfisher)

Relationship between Fish Tissue Filet and Whole body Hg

Cumulative Distribution Function (CDF) of Mean Site Fish Tissue Mercury Weighted population estimates from EMAP survey design

Extent of Big Fish Hg Contamination by Family Total Stream Length=305,000 km; 180,000 km with Big Fish

Summary Fish tissue mercury concentrations were most strongly related to trophic group and fish length not environmental factors, ecoregion, or site disturbance –Regional analyses must consider trophic group and size In terms of % Stream Length exceeding criteria Big Piscivores –93% > 0.1 µg/g –57% > µg/g Big Non-piscivores –26% > 0.1 µg/g –6% > µg/g

Summary (con’t) Fish tissue mercury concentrations in Western U.S. streams and rivers were found in a fairly narrow range, always above the detection limit (0.0024) –90% of the small fish and non-piscivores had Hg between 0.02 and 0.2 µg/g –High concentration “hot spots” (Hg > 0.5 µg/g) were very rare (< 2% of stream resource) This strongly suggests a broad diffuse source of mercury from atmospheric deposition.

Study was funded by EPA’s Environmental Monitoring and Assessment Program (EMAP) EMAP Regional Hg Survey Citations Oregon Streams: Peterson et al., Environ. Toxicol. Chem. 21: Mid-Atlantic Streams: Lazorchak et al., Environ. Toxicol. Chem. 22: Northeast Lakes: Yeardley et al., Environ. Toxicol. Chem. 17: