Monitoring and risk assessment of heavy metals surficial sediments using the 5-step sequential extraction process

ABSTRACT

Behaviour of heavy metals in the environment is widely acknowledged to be assessed by different physicochemical forms of presence rather than their overall concentration. In this study, Tessier 5-step sequential extraction technique was used to measure the trace metal (Mn, Cu, Zn, Fe, Pb, Co, Cd) fractions in surficial sediments in different seasons, in turn, analyse the risk posed by different fractions to the aquatic ecosystem. The findings reveal that residual fraction (F5) is in highest proportion (~44%) among the trace metals analysed. However, the proportion of carbonate and exchangeable fractions was comparatively higher (~24%), posing amajor risk to the aquatic ecosystem. Particle size v/s metal fraction scatter-plots showed that in the case of Cu, Fe and Mn, there is some form of both anthropogenic and natural pollution during the studied period, whereas, in rest of the metals, pollution is due to natural sources. Principal component analysis (PCA) led to the generation of 2 principal components (PCs), which accounted for approximately 80% of the total variance. PC1 and PC2 accounted for 45% and 35% of the total variance, respectively, which helped identify the pollution source as anthropogenic. Then, risk assessment code (RAC) revealed, Zn (41%), Mn (35%), Cu (35%), and Pb (27%) posed ahigher threat in drier months. In contrast, Co (40%) and Cd (48%) pose a higher threat with monsoon onset, showing variation of mobility of different metals in different seasons. Fe is the least mobile among the metals analysed, posing very little to the aquatic environment. Then, comparison with sediment quality guidelines (SQGs) reveals, although their potential hazard is high, they never surpass the SQGs. Thus, trace metal sediment contamination does not pose any risk to the river’s aquatic environment in the present study but calls for stringent measures employment in river pollution abatement.

KEYWORDS:

• Metal speciation
• spatio-temporal variation
• principal component analysis
• risk assessment code
• sediment quality guidelines

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.