Assessment of Heavy Metal Concentrations in Penang, Malaysia’s Wastewater Treatment Plants: A Wastewater-Based Epidemiology Approach

Abstract

Heavy metals and trace metals are among the most prevalent contaminants in sewage. Depending on the concentration and frequency of exposure, certain heavy metals are toxic, carcinogenic, and hazardous to humans. In this study, copper (Cu), nickel (Ni), zinc (Zn), iron (Fe), and cadmium (Cd) levels were measured in the collected wastewater samples from 10 selected domestic sewage treatment plants (STPs) in Penang, Malaysia in December 2021. All metals in the wastewater were determined using the atomic absorption spectrometric (AAS) method followed by the wastewater-based epidemiology (WBE) analysis. The mean concentrations of heavy metals in the wastewater samples were found to be in the following order (unit of mg/L): Fe > Ni > Zn > Cu > Cd (influent), and Fe > Ni > Zn > Cd > Cu (effluent). Among the metals, Fe concentrations were found to be the highest in effluent, with average values at 5.93 ± 5.319 mg/L, slightly over than a maximum permissible Fe concentration. Cadmium level in all STPs was significantly higher when compared to the maximum permissible Cd concentration (0.02 mg/L) allowed by Malaysia’s regulation, with an average of 0.13 ± 0.011 mg/L. Other metals concentration such as Cu, Ni and Zn in wastewater at the studied STPs showed low level and were considered safe. Using the WBE approach, the collected data were then calculated to estimate the population’s exposure consumption to heavy metals. Mass loading demonstrated high Fe exposure in all STPs but low Cd exposure, with the mean exposure of 1,924.86 ± 2451.772 and 46.91 ± 20.936 mg/1000p/d, respectively. Given the World Health Organization’s recommendation for tolerable weekly cadmium intake, the estimated human exposure to Cd in this study was particularly concerning, in addition to the lack of efficiency of Cd removal in the studied STPs. HIGHLIGHTS The order of the heavy metal mean concentrations in wastewater samples was Fe > Ni > Zn > Cu > Cd (influent), and Fe > Ni > Zn > Cd > Cu (effluent) The removal efficiency of the STPs followed the order: Cu > Fe > Zn > Cd > Ni The daily exposure rate of Fe was recorded as the highest exposure rate among other studied heavy metals (1924.7 ± 2451.772 mg/1000p/d) The daily exposure rate of Cd, estimated from the mass loads of total Cd, was found to be the lowest when compared to the other heavy metals (46.91 ± 20.936 mg/1000p/d) GRAPHICAL ABSTRACT