Background values for evaluation of heavy metal contamination in sediments in the Parnaíba River Delta estuary, NE/Brazil

• We report background levels of heavy metals in the sediments of Parnaíba River Delta.
• The measured values were compared with sediment quality standards.
• The Delta is characterized by the presence of low levels of heavy metals in sediments.
• The metal concentrations suggest a low probability of adverse effects to the local aquatic biota.

This study establishes regional background levels and upper thresholds (geochemical baseline) for Zn, Cu, Pb, Cr, Mn, and Fe from surface samples and profiles taken in 16 sedimentary environments of the Parnaíba River Delta estuary, NE–Brazil. Three approaches were applied to evaluate metal contamination: normalization to Fe, statistical analysis and sediment quality guidelines or environmental assessment criteria (TEL–PEL). Metal concentrations in sediments ranged from 2.4 to 31 mg Zn kg−1, 1.5 to 48 mg Cu kg−1, 1.3 to 28 mg Pb kg−1, 1.5 to 38 mg Cr kg−1; 145 to 1,356 mg Mn kg−1, and 0.3% to 2.5% for Fe. All metals showed positive correlations with the <0.63 μm sediment fraction, indicating a significant association with rich lithogenic sources of iron oxide–hydroxides. Results suggest a low probability of adverse effects to the local aquatic biota. The background values of the area were lower than those reported for other areas of the northeastern coast of Brazil.