MATERIALS AND METHODS Clams (R. cuneata) were collected at seven sampling stations
(Fig. 1) on Laguna de Pom once a year during three years (March 1987, April 1988 and
March 1989). Sediments were also taken in the last two years. Clams were collected with a
net, and sediments with a 0.1 m" Van Veen grab. All samples were transported under
refrigeration to CINVESTAV in Merida for further analysis. Hydrocarbon concentrations in
sediments were determined according to IOC/UNESCO (1982), and organisms following the …