North Carolina Eastern Regional Mercury Study: Results Michelle Woolfolk NC Division of Water Quality Presented April 19, 2004 at the CSSA Meeting

NC Eastern Regional Mercury Study Funded by USEPA grant (104(b)(3)) Goals 1.Evaluate levels of ambient mercury in surface water systems using low level techniques (Method 1631) 2.Estimate site-specific total mercury:methyl mercury translators to evaluate water quality criteria 3.Estimate site-specific water to fish bioaccumulation factors 4.Evaluate potential mercury loads from WWTPs Referred to hereafter as the ERMS

Ambient Surface Water Total Hg Goal 1: Ambient mercury levels No. of observations 46 Geometric mean (ng/L) 4.49 Median (ng/L)4.1 Range of concentrations 1.06 – 28.6 Standard exceeded in 11 % of samples.

Ambient Surface Water Total MeHg No. of observations 48 Geometric mean (ng/L) 0.32 Median (ng/L)0.241 Range of concentrations – 4.04 Goal 1: Ambient mercury levels

Ambient sediment Total Hg No. of observations 24 Geometric mean (ng/g) Median (ng/g)28.22 Range of concentrations 1.52 – Goal 1: Ambient mercury levels

Ambient sediment Total MeHg No. of observations 24 Geometric mean (ng/g) Median (ng/g)0.214 Range of concentrations – Goal 1: Ambient mercury levels

Ambient Hg residue: piscivorous fish Goal 1: Ambient mercury levels Black crappie

Ambient Hg residue: Omnivores and Insectivores Spotted sucker White catfish

Bioaccumulation factors Bioaccumulation is the uptake and retention of a chemical by a living organism as a result of either intake of food, drinking water, air or direct contact. (EPA 1994b) A bioaccumulation factor is defined as : BAF = Residue C(d) where Residue = concentration in wet tissue, mg/kg C(d) = concentration of chemical dissolved in H2O, mg/L Goal 3: Bioaccumulation

Bioaccumulation factors, cont. Can be species specific, size specific, or trophic level specific –Species specific: e.g., largemouth bass, black crappie, bluegill sunfish, etc. –Size specific: e.g., largemouth bass of length 40 cm –Trophic level specific: e.g., all of trophic level 3 Goal 3: Bioaccumulation

Largemouth bass bioaccumulation One of three species with a regional advisory by DHHS Caught and analyzed at every site in ERMS (makes site-to-site comparison possible) Calculate BAFs to all fish caught at a site and to a normalized 40-cm bass Allow variability in exposure concentration Goal 3: Bioaccumulation

Largemouth bass BAFs Goal 3: Bioaccumulation

40-cm Largemouth bass BAFs Goal 3: Bioaccumulation

What is the significance of BAFs? We use the BAFs to calculate the allowable water concentrations of MeHg(d) and ultimately Hg(t). Required to implement the AWQC for methylmercury Goal 3: Bioaccumulation

Target water column levels Evaluate human health endpoint, not wildlife Only evaluate to DHHS criteria Site-specific water column translators (i.e., MeHg(d)/MeHg(t) and MeHg(t)/Hg(t)) [less confidence in relationships between MeHg(d) and Hg(t)] Goal 3a: Target water levels

Target water column levels Goal 3a: Target water levels

Target water column levels, cont. Goal 3a: Target water levels

And now for the big picture…

Photo-toon by R. Johnson

Questions? Michelle Woolfolk Div. of Water Quality, Modeling Unit (919) ext. 505 Connie Brower Div. Of Water Quality, Standards Unit (919) ext. 572