Novel method to derive water quality criteria of metals

24 April 2018

Increasing contamination of marine ecosystems by metals such as mercury, cadmium, chromium and nickel has been a global environmental concern as high concentration of metals can be dangerous to marine organisms and humans along the food chain.

Setting water quality criteria of various metals is an essential step for assessing and regulating risk levels in the marine environment. The current method for deriving water quality criteria of metals is based on laboratory toxicity tests conducted at fixed conditions with stable temperature and salinity. However, these laboratory-derived criteria may not reflect the true picture as natural environmental conditions vary geographically and seasonally.

Professor Kenneth Leung (Croucher Fellowship 2000) from the University of Hong Kong and his team developed a novel empirical model for estimating the toxicities and deriving water quality criteria for metals and metalloids in coastal marine environments with variable temperature and salinity regimes. The team integrated temperature- and salinity-based species sensitivity distributions with quantitative ion characteristic relationships model and analysed real-time environmental data of sea surface temperature and salinity in different parts of the world. A list of provisional site-specific criteria for more than 30 metals and metalloids has been identified.

The research has been published in Environmental Science & Technology.

The results indicated that metal toxicities to marine organisms generally increase with seawater temperature, but found to be the lowest at an optimum salinity and increase when the salinity increases or decreases from the optimum level. If water quality criteria of a metal is derived from laboratory experiment conducted at optimum temperature and salinity, the criteria are unlikely to be protective to marine organisms living in an environment with higher temperature and lower salinity.

The results also suggested that marine species living in warmer waters in the tropical region, including Hong Kong and South China, are more susceptible to metal toxicities than their temperate counterparts. Governments in Asia such as Hong Kong and Korea often employ temperate toxicity data for deriving water quality criteria or directly adopt the criteria generated from Europe and North America. Using inappropriate temperate information might pose high uncertainty in the margin of safety.

The new method developed by the team can improve the management of metal and metalloids in coastal marine environments, as environmental authorities can now derive provisional site-specific criteria.

Professor Fengchang Wu, Director of State Key Laboratory of Environmental Criteria and Risk Assessment at Chinese Research Academy of Environmental Sciences, commented the results of this study will be of benefit in deriving water quality criteria of metals for different parts of marine environments in China and beyond.

“In Hong Kong, salinity in the western marine waters is relatively low due to freshwater discharge from the Pearl River, whereas the salinity in the eastern waters is consistently high because of dominant influence of oceanic currents from the Pacific Ocean and South China Sea. With consideration of such salinity differences, the method developed by the team can be readily applied to derive provisional site-specific water quality criteria of metals for enabling better protection to the eastern and western marine ecosystems of Hong Kong, respectively,” said Leung.

The research team will further investigate the influence of dissolved and suspended organic matter on toxicities of metals in seawater. They will also make use of field-based monitoring data of metal concentrations and marine biodiversity to validate their derived provisional criteria in different water bodies.


Professor Kenneth Mei Yee Leung obtained a BSc degree in Applied Environmental Sciences with first class honours at University of Portsmouth in England in 1993, and accomplished his MPhil study in Environmental Science at City University of Hong Kong in 1996. As a recipient of the Swire’s James Henry Scott PhD Scholarship, he undertook a doctoral study at University of Glasgow in Scotland and obtained his PhD in Marine Ecotoxicology in 2000. He was subsequently awarded The Croucher Foundation Fellowship, enabling him to conduct his 18-month postdoctoral study in ecological risk assessment of antifouling biocides at Royal Holloway, University of London in England (2000-2001).

To view Prof Leung’s Croucher profile, please click here