Metals in Crawfish - Aquaculture and the Environment: A Shared Destiny - page 207

(Richert and Sneddon, 2008). Numerous environmental studies have been done using
crawfish as a bio-indicator to monitor pollution. Crawfish have been useful as vectors to
monitor contaminants in water and soil because they are prolific, relatively sedentary,
easily recognizable and have a reasonably long life span. Additionally, they are in
constant physical contact with the water and surrounding soil. Their position in the food
web is high enough that some biomagnification can occur from eating contaminated
organisms from lower positions in the food web. Three recent studies have shown that
crawfish can be useful in monitoring the levels of a variety of metals. Schmitt looked at
the potential ecological and human risks associated with metals in fish and crawfish from
activities in the Tri-States Mining District (TSMD) in Northeast Oklahoma (Schmitt et al,
2006). Crawfish and six species of frequently consumed fish were collected in 2001-2002
from the Spring River and Neosho River which drain the TSMD. Whole crawfish were
analyzed in composite samples. Metals concentrations were found to be higher in the
samples from the sites most heavily affected by the mining and were lower in the
reference samples tested. The levels of Pb, Cd, and Zn exceeded current acceptable levels.
Human consumption of crawfish from the area was restricted based on the results of this
and previous studies. Monitoring contamination caused by a release of pollutants in 1998
in the Aznalcollar-Los Frailes, Spain mining region was the subject of a study (Sanchez
Lopez et al, 2004). Immediately following the spill there was much destruction to the
aquatic ecosystem of the Guadiamar River. Inductively coupled plasma-mass
spectroscopy (ICP-MS) was used to measure levels of Cu, Zn, Pb and Cd. American red
crawfish (Procamburas clarkii) were collected from various sites within the affected area.
The crawfish collected in the areas near the toxic release showed much higher levels of the
tested metals than did the crawfish collected from areas not directly affected by the spill.
Additionally, a translocation experiment using red swamp crawfish (Procamburas clarkii)
at different sites along the Guadiamar River was carried out in order to determine the
ability of this species as a bio-indicator of heavy metal (Cd, Cu, Zn, Pb, and As)
contamination (Alcorlo et al, 2006). Caged uncontaminated crawfish were placed at three
different sites which had different levels of contamination. The crawfish were then
harvested after six days and again after twelve days. Analysis by ICP-MS showed that in
as little as six days the crawfish were already accumulating the metals. The study also
showed that the metals not involved in crawfish metabolism tended to increase with
higher exposure and longer exposures.
10.2 Inorganics or metals
Inorganics or metals are most frequently determined in crawfish using spectrochemical
techniques such as flame and graphite furnace atomic absorption spectrometry (FASS,
GFAAS), inductively coupled plasma-optical emission spectrometry (ICP-OES), and most
recently inductively coupled plasma mass spectrometry (ICP-MS). It is beyond the scope of
this chapter to describe these widely used and accepted techniques and the reader is
referred to several texts that describe principles, instrumentation, and use of these
techniques. However, in most cases these spectrochemical techniques perform best when the
sample is in solution form, preferably in an aqueous or slightly acidic form. Typically
microwave digestion is using nitric acid is used to put the analyte in solution. The toxic
metals such as cadmium, mercury, and lead have been the most widely determined in
crawfish.