Bioaccumulation of heavy metals by Cyperus malaccensis and Spartina alterniflora in a typical subtropical estuary (Min River) of Southeast China

Abstract

To understand the bioaccumulation of heavy metals by Cyperus malaccensis (CM) and Spartina alterniflora (SA) in a typical subtropical estuary (Min River) of Southeast China, the concentrations of five metals (Pb, Cr, Cu, Zn, and Ni) in plants and sediments of CM and SA marshes were determined. Two experimental plots (no flooding plot and flooding plot) were established in the intertidal zone of the Min River estuary in July 2015, and, in each plot, in situ sampling was conducted in CM and SA marshes, respectively. The concentrations of heavy metals in all samples were determined by inductively coupled plasma mass spectrometry (ICP-MS) analysis. Vertical variations of the five metals differed between marshes or plots, and, in most cases, there was no evidence of grain-size composition (particularly for clay) and sediment organic matter (SOM) contributing to the sorption of significant amounts of metals in sediments of different marshes. Flooding regime was an important factor inducing the difference of metals in sediments of the two experimental plots. Heavy metal levels in different tissues of CM and SA differed within species or plots. For the five metals, the root was generally the main stock, and, as water condition changed from non-flooding to flooding, allocations of Pb, Cu, and Zn in CM and SA decreased while those of Cr increased. The accumulation factors [AFs] of heavy metals in different tissues of CM and SA also differed between species or plots. In most cases, the [AF]plant of different metals were less than 1, implying that the metal accumulations in CM and SA of the two plots were uncommon. This study found that Cu and Zn pollution in non-flooding conditions and Pb and Cu pollution in flooding conditions might be more serious, indicating that intertidal sediments might be severely contaminated by the three metals if effective measures are not taken to control the pollutant loadings of the Min River estuary in the future. Moreover, CM generally accumulated more Pb, Cu, and Zn while SA absorbed more Cr and Ni (particularly in flooding conditions), implying that, when determining environmental pressures, the two plants could be used as specified biological indicators.