A study of various factors affecting digestion of fish tissue prior to mercury determination

The effect of temperature on digestion, the acid combination and their quantities, and the time required for digestion of fish tissue were investigated using Hamour (Epinephelus tauvina) body tissue. Concentrations of Hg in fish tissue digested for four hours at 80 +/- 2 degrees C and 95 +/- 2 degrees C were statistically similar and significantly higher than in tissue digested at 60 +/- 2 degrees C. Eight acid combinations were investigated as digestion media and a 1:2 mixture of concentrated HNO3:H2SO4 proved to be the best. A quantity of 15 ml of this digestion media were found to be sufficient to digest approximately two grams of wet fish tissue. The use of 25 ml of digestion media resulted in significantly reduced Hg concentration whereas 10 ml was not sufficient to digest two grams of fish tissue. A digestion period of four to six hours at 80 degrees C was sufficient to oxidize the fish tissue. However, a two hour digestion resulted in reduced Hg values. Mercury determinations made from the samples prepared by the best combination of all the experimental conditions showed a good agreement with those of samples prepared in Teflon Acid Digestion Bombs. This study has pointed the necessity of developing a uniform standard procedure for digesting fish tissue prior to Hg determinations.