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Microcystin toxin in blue crabs in James River; Analysis of 2012 and 2013 monitoring

Microcystin toxin in blue crabs in James River; Analysis of 2012 and 2013 monitoring. Adjustment of Dry-Weight Data to Wet-Weight Concentrations.

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Microcystin toxin in blue crabs in James River; Analysis of 2012 and 2013 monitoring

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  1. Microcystin toxin in blue crabs in James River;Analysis of 2012 and 2013 monitoring

  2. Adjustment of Dry-Weight Data to Wet-Weight Concentrations The reported “dry weight” concentrations of microcystin were converted to “wet weight” concentrations by multiplying by 0.18 (the ratio of dry to wet weight in crab muscle samples, or 82% water) to assess the “as consumed” exposure to consumers .

  3. Wet Weight MC (ppm) in Crab Muscle July-September 2012 & 2013 • 90 crabs analyzed • Range; ND- 0.06541 • Median = 0.00126 • Mean = 0.00433 • Mean is equal to the 82nd percentile. Skewed high because of 3 high values.

  4. Blue Crab-Microcystin Concentrations 2012 & 2013 July-September (wet weight ppm) • Lowest = non detect (set at 0.001 to calculate means) • Median = 0.0013 • Mean = 0.0043 • 90th percentile = 0.0051 • August 2012 & 2013 Mean = 0.011 • Maximum = 0.062

  5. Microcystin in crab muscle fluctuates during season; but does not permanently bioaccumulate

  6. Standard EPA Recommended Exposure and Risk Assessment Methods Used World Health Organization provisional Tolerated Daily Intake (TDI) of 0.04 μg/kg body weight (converted to 0.00004 mg/kg) was used to assess potential health effects. TDI x bodyweight concentration of microcystin in crabs = allowable daily consumption rate

  7. Standard Calculation of Allowable Concentration of Toxicant in Fish & Shellfish RfD (TDI) (0.00004 mg/kg/day) X Body Weight fish consumption rate (0.0175 kg/day = 0.16 mg

  8. Potential for Exposure to Human Consumers Four scenarios investigated; Central tendency exposure estimates based on; 1. Median(0.0013) concentration of microcystin 2. Mean (0.0043) concentration of microcystin (standard value used in exposure and risk assessments) High end exposure estimates based on; 3. The 90th percentile (0.0051) concentration of microcystin 4. Highest monthly average (0.011) concentration of microcystin (August 2012 & 2013 mean)

  9. Screening Concentration Compared to Crab Concentrations at Rice Center

  10. Allowable Crab Meat Consumption Rates

  11. Estimates of Number of Crabs Needed to Equal the Allowable Consumption Rates (17.5 crabs yield 1 pound edible crab meat)

  12. What About Hepatopancreas Consumption? Approximately 7% of surveyed Virginia crab consumers reported eating hepatopancreas “most of the time”, 9% reported “some of the time” and 84% “never ate it”. To assess the consumption of a mixture of crab meat and hepatopancreas; the following was used; • A ratio of 0.813 muscle to 0.187 hepatopancreas • Mean concentrations (wet weight) of microcystin in muscle of 0.0043 PPM and 0.0234 PPM in hepatopancreas. (Means for Rice 2012 & 2013 July-Sept; = to 82nd %tiles)

  13. Allowable Consumption of Crab Meat and Hepatopancreas Mixture

  14. Crab prices; Lump Crab Meat $29.99 per pound. A bushel of male crabs goes for $199/bushel, $100/half bushel. Female crabs are available for $165/bushel, $85/half bushel.

  15. 24 Count Steamed Jumbo Male Hard Crabs $125

  16. Questions?

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