Heavy metal contamination and ecological risk in Futian mangrove forest sediment in Shenzhen Bay, South China

• Heavy metal concentrations and ecological risks are examined.
• Heavy metal concentrations decrease as Zn > Cr > Pb > Cu > Cd in sediments.
• The combinations of heavy metals have a 21% probability of being toxic.
• The sediments are polluted by heavy metals, especially for Cd.
• The heavy metals in sediments mainly exist in non-residual fraction.

Surface sediments in the Futian mangrove forest (South China) were analyzed for heavy metals including cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and zinc (Zn). The heavy metal distributions varied greatly in surface sediments, reflecting some sediment heterogeneity. The heavy metal concentrations decreased in the order of Zn > Cr > Pb > Cu > Cd. According to the mean probable effects level quotient, the combination of studied metals had a 21% probability of being toxic. The potential ecological risk index and geo-accumulation index also revealed high metal contamination. Cd was of primary concern due to its higher assessment values and potential for adverse biological effects. Multivariate analysis implied that clay and silt played a significant role in raising the levels of Cr, Cu and Zn. The percentage of mobile heavy metals was relatively higher, without considerable ecological risk to the biota based on the risk assessment code.