Metals in Crawfish - Aquaculture and the Environment: A Shared Destiny - page 212

determine the accumulation of lead as follows: gills>exoskeleton>organs>edible meat
Duplicates of the lead exposed crawfish were exposed to a concentration of approximately
10ppm (mg/L) selenium for a week to determine any adverse physiological effects. Within
48 hrs of exposure of selenium, the control crawfish were experiencing lethargy and signs of
paralysis. The same symptoms began to occur to the previously lead exposed crawfish
within 72 hours of selenium exposure. Analysis of the selenium exposed crawfish revealed
time dependent and tissue specific adsorption of selenium identical to the concentrations of
the lead exposed crawfish: gills>exoskeleton>organs>edible meat

After seven days of living in a complete state of paralysis, duplicates were placed in pure
water to determine the ability of the crawfish to purge the selenium and regain mobility.
Within 24 hours of purging, 88 percent of the paralyzed crawfish had regained full motor
skills. Analysis of the purged crawfish showed a significant decrease in the concentration of
selenium in the chitin rich exoskeleton and gills. However, the lead concentration in the gills
and exoskeleton of the purged versus non-purged crawfish did not show any significant
decrease indicating the covalent bond between the nitrogen and lead is much stronger than
the chelating ionic bond between the selenium and lead.

Currently in progress is the use of crawfish shells for the uptake and removal of metal ions
in aqueous solution (Vootla et al, 2011, and Beeram et al, 2011). Using ICP-OES, the samples
were analyzed for various concentration of lead at three different volumes, 40-mL, 500-mL,
and 3000-m.L. Crawfish shells , with the meat removed, were dried and pulverized to a 150-
mesh size. The results showed that with an increase in volume of water, the capacity to
remove lead by the crawfish exoskeleton by the same amount of shell powder decreased.
However, lead absorption by the same amount of shell powder in all phases was good in
terms of efficiency. The phase III study (3000-mL) showed that 0.5-g of crawfish absorbed
the maximum amount of lead. Moreover, both raw and boiled crawfish shells have the same
or similar capacity to uptake lead from water Vootla et al., 2011). Crawfish shell is a good
source of chitin constituting about 23.5 percent on a dry basis. Using this value, the number
of moles of chitin were calculated theoretically and compared to the number of moles of Pb
that it can uptake. For 0.5 g of crawfish shell powder taken, the amount of Pb up take per
gram of ground crawfish powder is calculated as shown in equation (1) and the values
shown in equation (2) and equation (3)

0.235 g of chitin

1 mole chitin molar mass of Pb 1 atom of Pb

(1)

weight of crawfish × × × ×

1 g crawfish molar mass I mole Pb Pb I monomer of chitin

chitin monomer

0.235 g 1 mole 207 g Pb 1 atom Pb

(2)

0.5 g × × × × = 0.1198g Pb

1 g 203 g I mole 1 monomer of chitin

0.1198 g Pb

(3)

= 0.240 g of Pb per 1g of crawfish shell = 240,000 ppm Pb

0.5 g of crawfish shell

These calculations were obtained by assuming this model as 100 % chitin efficient crawfish
shell. Based on 100% absorbance, one monomer uptaking one atom of Pb, the approximate
value obtained was 240,000 ppm. The experimental value (amount of Pb that has up taken)
obtained by analyzing the powder in this phase is approximately 200,000 ppm which is 83%.