Assessment of heavy metals in sediments of the Parnaíba River Delta in the semi-arid coast of Brazil

Studies related to heavy metal concentrations in coastal sediments are important to monitor and assess environmental health of estuarine ecosystems. Twenty-eight samples from Parnaíba River Delta, the largest open-ocean delta in the Americas, northeastern of Brazil were tested for heavy metals concentrations (Cd, Cr, Cu, Mn, Ni, Pb, Zn, Al and Fe), grain-size and easily oxidizable carbon. The relations of the heavy metals with sediment composition were evaluated using a multivariate statistical analysis. Sediment pollution assessment was carried out by enrichment factor (EF), geoaccumulation index (Igeo), contamination factor (CF) and potential ecological risk index (PERI). The average concentrations were 0.50 ± 0.09 mg Cd kg −1 , 6.95 ± 2.13 mg Pb kg −1 , 19.02 ± 8.75 mg Cu kg −1 , 23.20 ± 5.04 mg Ni kg −1 , 33.52 ± 6.82 mg Cr kg −1 , 43.99 ± 7.47 mg Zn kg −1 , 165.73 ± 86.71 mg Mn kg −1 , 2.93 ± 0.89% to Fe and 3.78 ± 1.17% to Al. The results indicate lower concentrations of heavy metals relative to limit concentrations defined by the Brazilian regulatory framework. The multivariate analysis reflected the binding of heavy metals to clay minerals and organic carbon. The different geochemical indices indicated sediments minimally enriched by metals and a low potential ecological risk level. Our assessment confirms the pristine conditions of Parnaíba Delta protected area to heavy metal contamination, except Igaraçú channel near Parnaíba city.