Contribution of Oil Industry Activities to Environmental Loads of Heavy Metals in the Tabasco Lowlands, Mexico

In Tabasco the petroleum industry pollutes soil recurrently by oil spills. We analysed Pb, V, Ni and Cr concentrations in water samples, and total metal contents and metal fractions in soil samples of contaminated and non-contaminated soils and in sediments. Besides, we determined Eh, pH, DOC and major ions in water and Eh, pH, C_org in soils and sediments. Sediments contained considerably larger heavy metal (HM) concentrations than soils. Local background concentrations of V, Ni and Cr in soils are larger than global means and oil spillages have not added these metals in quantities that exceed the natural variation. Spillage of formation water increases Pb concentrations in soils, particularly in mobile fractions. The contribution of the oil industry to HM loads is diluted by large fluvial water and sediment discharges and difficult to assess by comparison of total metal contents. Therefore, easily mobile metal fractions are much better indicators.