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This study investigated the water quality parameters (dissolved oxygen, electrical conductivity, salinity, pH, and temperature) and the mass flux of eight heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in five years (2015-2019) of the Houjing River. The river flows through a heavily-industrialized zone in Kaohsiung City in southern Taiwan. The surface water was sampled 4 times per year from five sampling locations: upstream sites (H1 and H2), industrial wastewater discharge point sites (H3 and H4), and downstream (H5). Our findings show that the water quality parameters improved in the study period, especially dissolved oxygen. However, some parameters, such as electrical conductivity (mean = 1152.50 ± 414.21 μS cm -1 ), were still higher than the Taiwan water quality irrigation standards. The heavy metal pollution was investigated in the aspect of mass fluxes and sources contribution. The spatial variation of the total heavy metal mass flux increased gradually from upstream to downstream, with H5 having the highest total mass flux of 74.1 kg d -1 . H2, located near an industrial zone, had a total mass flux of 33.7 kg d -1 and contributed to the most Ni, Cr, Pb, Zn, and Hg fluxes. This study indicates that the water quality improvements observed are still not enough to meet the regulations. Stricter enforcement is required as well as further investigation to identify any illegal pollution sources., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)

One of the most industrially affected rivers in Taiwan, the Houjing River, was studied in this research. The water and sediment samples were collected at five locations to measure the concentration of eight metals (As, Cd, Cr, Cu, Hg, Pb, Ni, and Zn). In order to assess the heavy metal contamination and its adverse biological effect, the heavy metal pollution index (HPI), the degree of contamination index (DC), the contamination factor (CF), the index of geo-accumulation (I geo ), and hazard quotients (HQs) were employed. The results showed that the Houjing River's water and sediment were contaminated with heavy metals. The annually averaged values of HPI (128.3) and DC (21.3) indicate that the water is unsafe for potable use and the sediment contamination level is at considerable degree of contamination. CF and I geo calculation show that Zn, Cu, and Cd are the three main metals contributing to heavy metal contamination in sediment. Evaluation of adverse biological effects suggests that Zn, Cu, and Ni are the major metals that cause adverse effects on organisms. This study provides an overview of the synergistic heavy metal contamination degree of the Houjing River and its adverse biological effects, which should be a reliable reference for future contamination control and management plans.