China's environment gets a health check
20 March 2008
Hepeng Jia /Beijing, China
Chinese chemists have provided a ground-breaking health report on the country's environment by accurately identifying pollutants, targeting pollution sources and exploring remediation strategies.
The findings appear in a special issue of the journal Environmental Toxicology and Chemistry, overseen by Tao Shu of the College of Urban and Environmental Sciences at Peking University, and Eddy Zeng of the Guangzhou Institute of Geochemistry of the Chinese Academy of Sciences.
'China is dealing with numerous challenges to sustain ongoing economic expansion while attempting to develop effective measures to protect the environment,' they write in an accompanying editorial. 'Economic growth in China has been achieved with excessive energy consumption and inefficient use of resources in many cases.'
The urgent need to address these concerns has prompted a significant increase in the Chinese government's funding of environmental science. 'Development of appropriate quality standards largely relies on quality research results,' Tao and Eddy add. 'China has long lacked reliable assessment standards that allow it to determine objectively the state of the environment.'
Balancing prosperity and pollution
One attempt to address this problem comes from Tao himself, who conducted a study into the presence of polycyclic aromatic hydrocarbons (PAHs) in the Pearl River Delta in south China's Guangdong Province. Economic prosperity in the region has sometimes been achieved at the cost of higher pollution levels in the environment.
PAHs, a group of chemicals mainly produced from fossil fuel burning, are problems worldwide, due to their carcinogenicity and extensive occurrence. However, Tao says that they are not subject to regular environmental surveillance in China.
Dicofol, a close relative of DDT, has been found in the Pearl River Delta
Generally, the composition of PAHs in the environment can help to determine the source of the emissions. The approach is based on the assumption that individual PAH compounds are diluted to a similar extent during environmental transport. But 'that assumption is not always valid,' explains Tao.
Tao and his colleagues tested 16 individual PAHs to show how their concentration profiles varied from source to environmental sink. They found that changes are influenced by factors like emission rates, degradation rates, adsorption coefficients, PAH concentrations in upstream surface water, and vapour pressure.
Another study on the issue, by Luo Xiaojun and colleagues at CAS's Guangzhou Institute of Geochemistry, has traced the residues of organochlorine pesticides (OCPs) in the Pearl River Delta.
OCPs, such as dichlorodiphenyltrichloroethane(DDT), are classed as endocrine-disrupting chemicals and were banned from agricultural uses in 1983. But Luo's study still found high levels of DDT in surface water samples, suspended particulate matter, and sediments. 'After long periods of decomposition, DDT residues should mainly exist in the form of its metabolite dichlorodiphenyldichloroethylene(DDE), but our study still found high level of DDT, raising the possibility of new DDT discharges,' Luo told Chemistry World.
He explains that although DDT is banned from direct use as a pesticide, it is still found in oil-based paints, and also used to make the chemically-related pesticide dicofol, which is mainly used on cotton plants. The studies clarifying the distribution of OCPs in different locations and periods and their transport are essential to develop proper controls on their use.
High levels of OCP contamination, along with heavy metals, can be found in other locations such as the Yellow Sea, as indicated by Liu Wenxin and colleagues from Peking University.
They found that levels of cadmium in bivalves exceeded recommended limits for marine organisms at 85 per cent of the Yellow Sea sites they sampled. Lead levels were similarly elevated in 73 per cent of cases. The scientists also found evidence of new DDT inputs at two sites in the north Yellow Sea - the potential sources involved industrial uses of DDT and dicofol.
Researchers have also studied the impact of pollutants on living organisms. Wang Zijian and colleagues from the Beijing-based Research Center for Eco-Environmental Sciences (RCEES), part of the Chinese Academy of Sciences, tested the influences of endocrine-disrupting chemicals such as 4-nonylphenol (4-NP) in sex-specific genes in the rare minnow fish, living in the Yangtze River.
'China still lacks a typical aquatic model animal to evaluate the level of toxicity in the environment,' says Wang. 'With its high sensitivity to the environment, rare minnow can be used in this way.'
In the study, exposure to different levels of 4-NP caused a corresponding down-regulation of a sex-specific gene called dmrt1. The researchers believe that this makes the gene's activity a sensitive biomarker that could help to uncover the molecular mechanisms underlying toxic response.
Xia Xinghui and Wang Ran from Beijing Normal University tested the biodegradation processes of PAHs in different sizes of sediments in the Yellow River.
The team found that the PAH-degrading bacterial population in water systems with coarse silt was lower than that with fine silt and clay, leading to the lower biodegradation rates. 'This study could offer insights for potential bio-processing of PAHs in the natural environment,' Xia told Chemistry World.
S Tao et al, Environmental Toxicology and Chemistry, 2008, 27
Also of interest
China's pollution headache
Chinese scientists have found concentrations of polycyclic aromatic hydrocarbons (PAHs) in some Chinese cities to be among the highest in the world.
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