Sample thermal decomposition followed by mercury amalgamation and atomic absorption has been
employed for the determination of methylmercury(MeHg) in fish. The method in volves HBr leaching of
MeHg, extraction into toluene,and back-extraction into an aqueous L-cysteine solution. Preliminary
studies were focused on the extraction efficiency, losses, contaminations, and species interconversion
prevention. The limit of detection was 0.018 mgg-1 (dry weight).The intraday precision for three
replicate analysis at aconcentration of 4.2 mgg-1 (dry weight) was 3.5 percent, similar to the interday
precision according to analysis of variance(ANOVA). The accuracy was guaranteed by the use of for tified
samples involving 83–105 percent recoveries , and certified reference materials TORT-2(lobster
hepatopancreas) and DORM-3(dogfish liver), providing 107 and 98 percent recovery of certified values.
The greenness of the method was also evaluated with the analytical eco-scale being obtained a final
score of 73 points which means anacceptable green analysis.The method was applied to fifty-seven
market samples of different fish acquired from local markets in several sampling campaigns. The content
of MeHg found varied between 0.0311 and 1.24 mgg-1 (wet weight), with values that involve 33–129
percent of the total mercury content. Someconsiderations about food safety wereal so done taking into
account data about Spanish fish consume and Tolerable Weekly Intake(TWI) established for MeHg.