Professor Ming Hung Wong talks about the persistent toxic substances (PTS) in our water resources and how scientific findings can support policymaking in order to control the pollutants. Professor Wong is an Advisor of the Education University of Hong Kong, Emeritus Professor of Hong Kong Baptist University, and Chang Jiang Chair Professor of the Ministry of Education, China. He is also the Editor-in-Chief of Environmental Geochemistry and Health.
My main research areas covered: (1) Environmental health and toxicology related to Persistent Toxic Substances (PTS), (2) Remediation of contaminated sites, and (3) Resource reuse, with a focus on food waste. The first research topic is more related to SDG 6 on water sanitation through the studies on the geochemical cycles of PTS.
The persistent toxic substances (PTS) include toxic metal/loids (arsenic, cadmium, copper, lead, mercury, zinc, etc.), persistent organic pollutants (POPs): dichlorodiphenyltrichloroethane (DDT), pentabromodiphenyl ether (PBDE), dioxins/furans (PCDD/F), polychlorinated biphenyls (PCB), etc., and emerging chemicals of concern (pharmaceutical and health care products, microplastics, bisphenol A, phthalates, etc.). Polyaromatic hydrocarbons (PAH) are generated from industrial combustion and opening burning processes but are not included in the Stockholm Convention control list. Some PTS, e.g., arsenic and mercury, can be emitted from the natural environment. However, human activities (such as metal mining/smelting and other industries) have aggravated their releases over the past few decades. These PTS enter our food production systems due to the contaminated water used for irrigation and fish culture, posing health hazards worldwide (e.g., high arsenic in paddy rice and mercury in fish).
These PTS are released to the environment in different activities and sources, from domestic, industrial, and agricultural runoff. They will eventually enter our sewage treatment works designed to decompose organic matter into inorganic matter (aerobic and anaerobic digestion) but not toxic chemicals. Some PTS could enter into food chains by discharging sewage effluent into the water bodies and applying sewage effluent and sludge for farming. Our studies investigated the removal efficiencies of a wide range of PTS in the conventional biological treatment and the enhanced chemical treatment works (commissioned by the Drainage Services Department of Hong Kong). Results revealed that the removal efficiencies of different PTS in sewage treatment plants are varied widely. Some PTS, such as flame retardants (PBDE), may even change their congeners with a higher portion of more toxic congeners. Another study on the treatment efficiencies of microplastics is underway, but the removal efficiencies are expected to be relatively low.
Over 200 industrial compounds and pollutants (total 287 chemicals) were detected in 10 newborn babies (umbilical cord blood) in 2004 in the USA (EWG, 2005). The PTS included DDT, PBDE, PFOA/PFOS, PCB, PCDD/F, with 180 out of 287 chemicals causing cancer in humans or animals, 217 are toxic to the brain and nervous system, 208 cause congenital disabilities or abnormal development in animals. In South China, we have also observed high levels of different POPs (DDT, PCB, PCDD/Fs, PBDE) and toxic metals (mercury) in human milk, blood serum, and adipose tissues. Frequent fish diets seem to link with higher concentrations of mercury and POPs in body tissues.
The practice of green agriculture and aquaculture would be essential to avoid using certain pesticides and chemicals for food production. Appropriate plants, associated microbes, and organic amendments (compost and biochar) can clean up contaminated soils for farming and contaminated sediments (fish ponds and mariculture sites) for fish culture. We could also consider developing active urban agriculture and aquaculture for safe and quality food production using the locally generated waste (e.g., food waste instead of fishmeal which is often contaminated for fish culture). This could help trim the carbon and ecological footprint. Integrating food production (fish and crops) with wetlands for water purification would be possible, but more research is needed.
The Pearl River Delta, the most developed region of China, is also one of the mega deltas worldwide. The area has been known as “Homeland for rice and fish”. Still, it has converted to the world center for electronic/electrical, textile, footwear, and pharmaceutical products, in addition to its active mining industries, e-waste recycling, and overuse and abuse of fertilizers. Consequently, many toxic chemicals have entered our food production systems, linked with their high body loadings and health symptoms. Data gaps exist concerning some emerging chemicals of concern, e.g., antibiotics, pharmaceutical, healthcare products, flame retardants, etc. To better manage toxic chemicals, especially those commonly found in food items: e.g., arsenic and heavy metals in rice and vegetables; mercury and different POPs in fish, and POPs (including dioxins/furans) in various food items, there is an urgent need to establish a regional list of toxic chemicals, paying attention to their sources, fates and environmental and health effects, due to specific regional conditions (based on my 2nd UN project).
There are several relevant conventions dealing with various wastes and chemicals globally: (1) The Basel Convention (Control of Transboundary Movements of Hazardous Wastes and their Disposal), (2) the Rotterdam Convention (Prior Informed Consent Procedure for Certain Hazardous Chemicals and Pesticides in International Trade), (3) Convention on Long-Range Transboundary Air Pollution, (4) Minamata Convention on Mercury, and (5) the Stockholm Convention on POPs. The European Union has introduced regulations to control the recycling of electrical and electronic equipment (EEE) waste and prohibit certain toxic substances in manufacturing EEE. Not all the conventions are effective. For example, the illegal transport of hazardous wastes and chemicals from developed to developing countries is serious. This is especially true with the transport of electrical and electronic waste (e-waste) across international boundaries. The USA produces a large amount of e-waste but has not ratified the Basel Convention. The e-waste in receiving countries is recycled using primitive techniques, emitting many toxic chemicals, adversely affecting the environment and human health. Our food basket analyses conducted in two major e-waste recycling sites showed that the local food items, especially fish, are highly contaminated by dioxins and flame retardants and linked with high body (hair, milk, placenta) loadings of these toxic chemicals. After China banned the entry of e-waste, it is now transported elsewhere, repeating the same mistakes in the receiving countries.
The ‘Regionally Based Assessment of PTS’ (my 1st UN project) identified the data gaps of the sources, fates, and effects of PTS in ten different world regions. Effective modelings to predict transboundary movements of PTS are needed as some PTS (such as DDT and PCB) could travel long distances through air and water. Standardizing sampling, analyses, presentation of results, etc., across various regions is essential to compare data. In some areas, technical and financial assistance is critical. The results complemented the Stockholm Convention on POPs (signed in 2001 and became effective in 2004) to protect human health and the environment. The principal purposes were to reduce the production, usage, and concentrations of POPs in environmental media and human bodies. Each country has to implement its national plan and prioritize its strategies when dealing with different POPs. A group of Swedish scientists who monitored various POPs in human milk throughout the past few decades noted that the concentrations of DDT, PCB, and PCDD/F had been declined, but PBDE increased. Fortunately, PBDE (together with other toxic chemicals such as lindane, a pesticide) was added to the control list as it fulfills the criteria: toxic, persistent, and can travel long distances. This is an excellent example of how research results could be utilized for policy-making for the worldwide control of POPs.
Prof. Wong is currently an Advisor (Environmental Science) of the Education University of Hong Kong, Emeritus Professor of Hong Kong Baptist University, Chang Jiang Chair Professor of the Ministry of Education, China, and Editor-in-Chief of Environmental Geochemistry and Health. His research interests include ‘environmental health and toxicology, ecological restoration, and resource reuse.’ According to the World’s Top 2% Scientists (Stanford University) list, he is ranked No. 6 (career-long) and the top Chinese scientist globally in 2020 and 2021 under Environmental Sciences.