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

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 .

Wet Weight MC (ppm) in Crab Muscle July-September 2012 & 2013

90 crabs analyzed Range; ND- 0.06541Median = 0.00126Mean = 0.00433Mean is equal to the

82nd percentile. Skewed high because of 3 high values.

1 7 13 19 25 31 37 43 49 55 61 67 73 79 850.00000

0.01000

0.02000

0.03000

0.04000

0.05000

0.06000

0.07000

Blue Crab-Microcystin Concentrations 2012 & 2013 July-September (wet weight ppm)Lowest = non detect

(set at 0.001 to calculate means)Median = 0.0013Mean = 0.004390th percentile = 0.0051August 2012 & 2013 Mean = 0.011Maximum = 0.062

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

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 760.00000

0.01000

0.02000

0.03000

0.04000

0.05000

0.06000

0.07000

July-September 2013 Rice; Microcystin in Crab Meat

(ug/g Wet weight)

Standard EPA Recommended Exposure and Risk Assessment Methods UsedWorld 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

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

Potential for Exposure to Human Consumers

Four scenarios investigated;Central tendency exposure estimates based on; 1. Median(0.0013) concentration of microcystin2. 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)

Screening Concentration Compared to Crab Concentrations at Rice Center

Screening Concen-tration

median mean 90% August0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

Allowable Crab Meat Consumption RatesMicrocystin in

Crab Meat (mg/kg)

Pounds per day

Pounds per week

Pounds per

monthMedian; 0.00139

4.44 31.09 135.0

Mean; 0.0043

1.44 10.05 43.64

90th %tile; 0.0051

1.21 8.47 36.80

August Mean:

0.011

0.56 3.93 17.06

Estimates of Number of Crabs Needed to Equal the Allowable Consumption Rates

(17.5 crabs yield 1 pound edible crab meat)Concentration

scenarioAllowable pounds/da

y

# Crabs per Day

# Crabs per Week

# Crabs per Month

Median 4.44 78 544 2,365

Mean 1.44 25 176 767

90th %tile 1.21 21 148 645

Highest Month Mean

0.56 10 69 298

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 hepatopancreasMean 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)

Allowable Consumption of Crab Meat and Hepatopancreas Mixture

Consumption per day

Consumption per Week

Consumption per Month

Pounds 0.78 5.5 23.75

Number of Crabs

11 80 344

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.

Crab prices;

24 Count Steamed Jumbo Male Hard Crabs $125

Questions?