Thallium in the marine environment: First ecotoxicological assessments in the Guadalquivir estuary and its potential adverse effect on the Donana European Natural Reserve after the Aznalcollar mining spill (SW Spain)

Thallium (Tl) is an extremely toxic but little-studied element in the marin e environment and practically no information has been reported on the level s of Tl in marine organisms. After the Aznalcollar mining spill (April 1998 ), high levels of metals were put into the environment. This acid-contamina ted medium was responsible for the initial pollution effects measured in th e Guadiamar River, which is an affluent of the Guadalquivir River and very close to the biggest natural reserve in Europe (Donana). Four different spe cies were used in the monitoring from April to September 1998 and a sedimen t field bioassay to check bioacumulation was performed. We present the firs t ecotoxicological evaluation of the mining spill in the Guadalquivir River , with reference to Tl, a little-known metal. Also, Ph and Cd data were com pared tb Tl during field sediment testing. Results show low levels of this metal in all of the organisms studied and they do not show any increase in the level of this metal, ranging from 40 to 90 ng g(-1), 80 to 210 ng g(-1) , 15 to 98 ng g(-1) and 75 to 125 whole body dry weight for Scrobicularia p lana, Liza ramada (muscle), Crassostrea angulata and Uca tangeri, respectiv ely. These are the first field data of Tl concentration measured using estu arine organisms. Field sediment toxicity test results confirm those obtaine d during the monitoring: Tl is not bioaccumulated by the organisms (C. angu lata) used in the test. The sequence in bioaccumulation of metals was Cd > Ph > TI. Both studies, bioaccumulation and sediment toxicity, should be mai ntained during the next few years to really evaluate the potential effect o f the mining spill on the ecosystem and society.