Grey water footprint model of heavy metal based on the hazard quotient

Abstract

The traditional Grey Water Footprint (GWF) model, rooted in the assumption that the hazard of each pollutant is independent, faces a limitation when dealing with heavy metals, whose hazards to aquatic organisms accumulate. The objective of this study is to develop a GWF model that reflects the cumulative threat posed by heavy metals to aquatic organisms, using the Hazard Quotient (HQ) as a foundation. The model comprises three parts: (i) defining the minimum virtual water volume required to control the HQ within the allowable limits, which includes long-term GWF (L-GWF) and short-term GWF (S-GWF); (ii) calculating the hazard level of heavy metal pollution (HHL); and (iii) determining the contribution rates of each heavy metal to L-GWF and S-GWF. The evaluation results of the heavy metal pollution discharged from the Guixi Smelter show that (i) The GWF of heavy metals from the Guixi Smelter decreases dramatically in 2014, with L-GWF and S-GWF of 2.39 and 0.22 billion m3, respectively, which are only 49.9 % and 47.1 % of L-GWF and S-GWF in 2013. (ii) The HHL values in 2012 and 2013 are 1.52 and 1.43, respectively, with a grade of “moderate.” In contrast, the HHL values in 2014 and 2015 significantly decrease to 0.82 and 0.74, respectively, both with a grade of “low”. (iii) The L-GWF contributors of heavy metals in the Guixi Smelter are Cu > Cd > Pb, and the S-GWF contributors are Cu > Pb > Cd > As. (iv) The GWF model based on HQ overcomes the limitations of conventional GWF and provides an effective assessment of the cumulative heavy metal hazards to aquatic organisms.