EPA 1997 — Arsenic and Fish Consumption (EPA-822-R-97-003)
This December 1997 report from EPA’s Office of Science and Technology summarizes available data on arsenic concentrations and speciation in fish and shellfish, then uses that data alongside USDA dietary intake survey records to estimate inorganic arsenic (iAs) exposure across six fish-consumption scenarios. The report was produced to address whether the then-current MCL of 50 ppb for arsenic in drinking water could also serve as an Ambient Water Quality Criterion under the Clean Water Act and to determine whether fish and shellfish consumption from the same waters adds materially to iAs exposure. The central finding is that more than 95% of arsenic in marine fish and shellfish is present as organic species (primarily arsenobetaine), a compound that is metabolically inert in mammals and rapidly excreted, so that dietary iAs exposure from fish and shellfish is low relative to drinking water exposure for most population groups.
Key numbers
Total arsenic in marine finfish (literature compiled by Chew 1996, Ballin 1994, Lawrence 1986):
- Range across species: less than 1 to 64 ppm (wet weight); most species 0.6–37 ppm
- Two outliers: skate (64 ppm), stingray (17 ppm), both with near-zero inorganic fraction
- Anchovy, tuna, sardines, hake, sole from commercial sources (Lopez 1994): 0.82–7.76 ppm tAs
Total arsenic in shellfish:
- Chew 1996 dataset: average 0.2–126 ppm (mollusks highly variable, 1–126 ppm across 20 samples)
- Ballin 1994: 2.6–21 ppm across four species; highest in lobster
- Lawrence 1986: lobster 5.2 ppm, shrimp 20.8 ppm, scallop 0.68 ppm
Freshwater finfish (much lower):
- Ballin 1994 (Germany rivers/hatchery): detection limit to 1.5 ppm tAs; 22 of 23 samples below 0.3 ppm
- Lawrence 1986 (Ontario/Alberta): 0.007–0.24 ppm tAs
Inorganic arsenic fraction:
- Marine fish: less than 4% iAs in all but three species (shark 9.5%, sturgeon 6.9%, sucker 8.5% per Chew 1996); 23 of 42 fish samples had iAs below detection
- Shellfish: less than 3% iAs in all but one case per Chew 1996; 18 of 50 shellfish samples below detection
- Arsenobetaine accounts for 96–100% of tAs in marine finfish (Ballin 1994); arsenocholine estimated at less than 1% of tAs
Bioconcentration: EPA BCF for arsenic in mixed fish/shellfish diet = 44; shellfish-specific BCF (oyster) = 350, freshwater fish BCF = 4. From 50 ppb arsenic water: estimated tAs in edible tissue = 2.2 ppm; estimated iAs (at 4% maximum fraction) = 0.09 ppm; at median 0.4% fraction = 0.01 ppm.
iAs exposure scenarios (Table 2, USDA 1989–1991 dietary intake data):
- High fish/high arsenic (99.9th percentile consumer, max 4% iAs, 461 g/day): 41 µg iAs/day
- High fish/average arsenic (99.9th percentile, 0.4% median iAs, 461 g/day): 4 µg iAs/day
- Average fish/high arsenic (50th percentile, 4% iAs, 42 g/day): 4 µg iAs/day
- Average fish/average arsenic (50th percentile, 0.4%, 42 g/day): 0.4 µg iAs/day
- High fish with shellfish preference (99.9th percentile fish/125 g/day shellfish, 4% iAs): 90 µg iAs/day
- General population (6.5 g/day normalized, high arsenic): 0.6 µg iAs/day
Combined iAs exposure (fish/shellfish + drinking water at 20 ppb high/5 ppb average, 2 L/day):
- General population (fish + 5 ppb water): ~11 µg iAs/day
- General population (fish + 20 ppb water): ~41 µg iAs/day
- High shellfish preference (fish/shellfish + 20 ppb water): ~130 µg iAs/day
Methods (brief)
Literature review of published arsenic speciation data for fish and shellfish (Ballin 1994, Chew 1996, Lawrence 1986, Lopez 1994 as primary data sources). Exposure scenarios derived from USDA Continuing Survey of Food Intake 1989–1991 for fish-consuming subpopulations and general population (6.5 g/day normalized). Inorganic arsenic fractions applied from Chew 1996 and other speciation studies. Arsenic in edible tissue estimated from EPA bioconcentration factors against ambient water at 50 ppb. No original analytical measurements were conducted; this is an exposure assessment compiling existing data. Key limitation: BCF derived from laboratory inorganic arsenic spikes, not natural trophic cycling; may underestimate marine species accumulation.
Implications
Certification: The speciation data are fundamental to the wiki’s iAs-vs-tAs rule for seafood. Because more than 95% of arsenic in marine fish is arsenobetaine (not iAs), total arsenic measurements in marine finfish are not an appropriate proxy for iAs exposure. HMT&C product pages for seafood must specify whether measurement is tAs or iAs; using tAs values as iAs is a major over-estimate for marine species. The report also establishes that freshwater fish have materially lower total arsenic and a different (uncharacterized) organic arsenic compound, warranting a distinct treatment on freshwater-fish.
Courses: Illustrates why speciation matters: a 37 ppm tAs value in a marine fish (catfish, Ballin 1994) sounds alarming but carries less than 4% as iAs (~1.5 ppm iAs), a fraction that is metabolically inert. Useful teaching case for the iAs/tAs distinction.
App: The app should treat marine seafood as a low-iAs matrix unless speciation data indicate otherwise. Shellfish (especially mollusks) have higher tAs but still low iAs fraction. The 4% maximum and 0.4% median iAs fractions are the appropriate conversion factors pending species-specific speciation data.
Regulations: The Ambient Water Quality Criterion context is US-specific (CWA 0.018 ppb vs MCL 50 ppb at time of writing). The report predates the 2001 MCL revision to 10 ppb; downstream regulatory pages should note that the 50 ppb water-arsenic scenarios in this report are now historically high for most US public water systems.