Metal and metalloid pollution in shelf sediments from the Gulf of C′adiz (Southwest Spain): Long-lasting effects of a historical mining area

The Gulf of C ' adiz is an area historically affected by acid mine drainage and also by the discharge of two important rivers, the Guadiana and the Guadalquivir. Metal and metalloid (As, Cd, Hg, Pb, Zn, Cu, Cr, Ni, Mn, Fe, Al and Li) concentrations were measured in 33 surface sediment samples, collected in the continental shelf, inside the Ria de Huelva and the Bay of C ' adiz, to assess the metal pollution status of this area. Geographical distribution was identified for different groups of metals: Cu, Cd, Zn, Hg and As were mainly associated with discharges of the Tinto and Odiel rivers, which have been historically affected by mining, into the Ria de Huelva. Sediments inside this Ria presented the highest concentrations of the whole area for these metals, and enrichment factors revealed that Hg and Cu pollution spread up to 20 km away from the mouth of this Ria, into the continental shelf. On the contrary, the distribution of Ni, Cr and Mn did not show a clear gradient with distance from a pollution source, and was mainly explained by geochemical factors, such as their association with fine materials. The comparison of metal concentrations with sediment quality guidelines, predicts that adverse ecological effects due to the metal pollution may be occurring in a group of stations located in the northwest corner of the studied area. Local background levels for metals in the Gulf of C ' adiz were proposed and the information obtained will be useful to identify those areas where sampling must be intensified in ongoing Marine Strategy Framework Directive (MSFD) monitoring programs. These results corroborate that metal pollution is still a serious problem in the Gulf of C ' adiz.

Automated summary

This study assessed the metal pollution status of the Gulf of C' adiz by measuring metal and metalloid concentrations in surface sediments. The distribution of metals such as Cu, Cd, Zn, Hg, and As was mainly associated with historical mining activities, while Ni, Cr, and Mn showed a different distribution pattern explained by geochemical factors. The comparison of metal concentrations with sediment quality guidelines indicated adverse ecological effects in a specific area. These results highlight the ongoing issue of metal pollution in the Gulf of C' adiz.