among the trace elements , arsenic appears to possess a unique position in the environment . 
 when comparing terrestrial and marine organisms there seems to be a significant difference between both level and chemical forms of arsenic . 
 the level of arsenic in terrestrial organisms is seldom above 1 ppm ( dry material ) whereas the corresponding values for marine organisms vary from several parts per million up to more than 100 ppm . 
 furthermore , results so far show that marine organisms are able to convert inorganic arsenic into organic arsenic compounds . 
 no evidence points to a corresponding ability in the terrestrial ones . in the aquatic organisms the arsenic is present as both lipid soluble and water soluble compounds . 
 the water - soluble organic arsenic compounds have a basic character and are very stable to chemical and metabolic breakdown.imagesfigure 5 .