China’s Coast: Unbearable Weight of Heavy Metals

By Tan Qiaoguo 9 July, 2014

Toxicologist Dr. Tan laments over the amount of heavy metals carried by China's rivers into her coastal waters

Over a third of China’s coastal waters are polluted; the North is worse than the South; cities & fisheries affected
Research shows rising trend in heavy metals discharge
Divergent trends: direct discharge into the sea is falling whilst heavy metals carried by rivers to the sea are rising

“… if the government can better manage pollution into rivers … pollution of China’s coastal waters can still be salvageable”

Heavy metal pollution in China’s seas remains grim with unabated annual discharges. The MEP’s 2011 Coastal Environmental Quality Report, says more than a third of China’s coastal waters suffer light to heavy pollution. If the government can better manage pollution at the source, in particular discharge into China’s rivers, it can control the spread of pollution to the marine environment and pollution of China’s coastal waters can still be salvageable.


Heavy metals in the environment

Whether we like it or not heavy metals are natural components of the earth. Unlike organic pollutants which are biodegradable, heavy metals remain constant in nature. The weathering of rocks, dust and volcanic eruptions release heavy metals into the air and waterways and rivers carry them from the land into the ocean. Very basically, heavy metals in surface waters are eventually absorbed into particulate matter and along with sediment sink; time turns sediment layers into rock and the heavy metals are once again imprisoned.

Human activities have disrupted this natural cycle: mining for ore, metal smelting, metal production and waste have released the circulation of heavy metals into the environment, increasing their concentration in water, soil and air. Our impact on the environment might appear small compared to the likes of tsunamis, earthquakes and other forces of nature, but in releasing heavy metals into the environment we have arguably surpassed nature herself.

More than a third of China’s coastal waters are polluted

The MEP’s 2011 Coastal Environmental Quality Report covers 281,012km2 of China’s coastal waters, an area greater than the United Kingdom. Of this, 37.2% was found with light to heavy pollution. Worryingly, 16.9% was found with heavy pollution (Grade IV+). (Editor’s note: sea water quality standards differ from freshwater quality standards – more on conflicting measurements here)

“… heavy metal pollution in China’s coastal waters is not evenly distributed and mostly persist in the coastal areas where major cities and fisheries are located”

What’s worse is that heavy metal pollution in China’s coastal waters is not evenly distributed and mostly persist in the coastal areas where major cities and fisheries are located.

According to a national research project, “Comprehensive Survey & Evaluation of China’s Coastal Environment”, heavy metal pollution levels are worse in the North than in the South. Heavy metal pollution in Bohai Sea is the worst, with concentrations significantly higher than those in the Yellow Sea, East China Sea and South China Sea.

Today, high levels of heavy metals in seafood are a concern and with increasing coverage by the media, it seems like oceanic heavy metal pollution is getting worse, but is it?

Biogeochemical research shows a significant increase in heavy metal concentrations

In addition to yearly monitoring, there are several other ways to analyze heavy metal pollution trends in the sea. One method is to analyze the sediments at the bottom of the sea. Since heavy metals in the water accumulate in sediments, each deposited layer records the heavy metal content at that time. So if we drill a mud column and analyze each layer, we can get a clear understanding of the historical trend of heavy metal pollution of up to a hundred years ago.

Pearl River Delta sediment columns show concentrations of lead and zinc have increased significantly in the last 20-30 years

In 2000, sediment sample columns taken from several points along the Pearl River Delta were studied. The results showed that although the specific data for each sampling point varied from year to year, the overall historical trend over the past 100 years is clear.

In the last 20-30 years, concentrations of lead and zinc have increased significantly; whilst copper and nickel showed no rise in concentrations with fluctuations within a narrow range.

Daya Bay coral samples show accelerated growth with zinc concentration levels rising by 3-5x in the last 10-20 years

Another method is to monitor the growth of corals. The skeletons of corals are formed from calcium secretion layer by layer, like tree rings. The heavy metal content in the coral skeleton and that in the water can be positively correlated.

By analyzing coral samples near Daya Bay in Guangdong, researchers found that the relative concentrations of zinc found in coral skeletons has risen steadily in the past 30 years. In fact, the last 10-20 years show accelerated growth with zinc concentration levels rising by 3-5x.

Direct & indirect heavy metal pollution of coastal waters

The main sources of coastal pollution are:

  1. Direct Discharge – primarily from municipal and industrial wastewater from coastal cities & industrial parks; and
  2. Indirect Transportation by Rivers to the Sea – rivers carry heavy metals discharged upstream into coastal waters.

Tech innovation & scientific management can cut off the correlation between economic development & pollution

Seemingly logical reasoning is that heavy metals discharge will continue to rise and pollution worsen as China steadily grows its economy. However, technological innovation and scientific management could cut off the correlation between economic development and pollution. This has been demonstrated for heavy metals directly discharged to the sea where there have been efforts to reduce direct discharge from industrial & municipal sources into the sea, in particular through better management of centralized discharge points and large industrial enterprises & parks.

Direct discharge into the sea is controlled & falling …

A recent study, done by researchers from the University of Michigan and Tsinghua University, shows that aquatic heavy metal discharge per unit GDP growth has decreased during 1992-2007. In fact, from 2007 to 2012, the absolute amounts of direct heavy metals emissions into the sea have started to fall whilst GDP is still on the rise. According to national statistics (Environment Statistical Report), the discharge of lead, mercury, cadmium, hexavalent chromium and arsenic in industrial wastewater all present downward trends from 2003 to 2011.

According to 2011 statistics published by the MEP (only made publically available  in 2014), 432 discharge-points along the coast, discharging 4.74 billion tonnes of wastewater were monitored and heavy metals discharged in industrial wastewater and municipal sewage directly into the sea in 2011 were as follows:

Heavy Metals Directly Discharged into Coastal Waters (2011)

However, this is direct discharge into the sea. Indirect discharge carried by the rivers to the sea is much greater – in some cases, hundreds or even thousand times higher.

But amounts carried by rivers to sea are hundreds & thousand times higher and rising …

In recent years, although the direct discharges have been controlled and are declining, heavy metal discharge delivered by the rivers remain significant. It is clear from the table below that direct discharge is negligible when compared to the amount of heavy metal carried by the rivers to the sea:

Heavy Metals Carried by Rivers to the Sea (2006-2011)

Such disparity is not difficult to imagine as it is easier to control discharge pipes and big industrial enterprises & parks along the coastline than dispersed polluting SMEs along China’s rivers across provinces.

The MEP’s Coastal Environmental Quality Reports in recent years recognizes this divergent trend; that direct heavy metal discharge from industrial wastewater and combined sewage to the sea has declined, whereas amounts carried by rivers to the sea reflecting upstream pollution has significantly increased.

… heavy metals flowing into the sea remains unabated… putting enormous pressure on our marine ecosystems  …

… the situation remains grim.

Currently, amounts of heavy metals flowing into the sea remains unabated. Such pollution puts enormous pressure on our marine ecosystems and the situation remains grim.

We still have more than 40,000 km2 of clean waters from which we can produce high-quality seafood so there is no need to panic yet. However, we need to start tackling pollution at source so as to control and reduce amounts carried by rivers to the sea to allay increasing fears over heavy metal pollution in seafood.

Further reading

  • Pollution: Is Data Real?: Inconsistencies in the recording and reporting of pollution data begs the question: is the data real? With 7,700 tonnes of lead in China’s rivers carried to the sea unaccounted for in 2011, is the real state of environment worse than we thought?
  • 2013 State of Environment Report Review: MEP’s 2013 State of Environment Report says the ‘overall environmental quality was average’ but a closer look reveals mixed news, whilst discrepancies found in sets of pollution data add uncertainty of the real state of the environment
  • Heavy Metals & Agriculture – Check out China Water Risk’s overview of the status of heavy metals discharge into wastewater, priority provinces, overlap with agriculture sown lands, crops exposed and industries targeted for clean-up
  • Crying Lands: China’s Polluted Waterscapes – Award-winning photographer Lu Guang shares his journey in documenting  sensitive social, health & environmental issues in China. See the tangible linkages through his heart-rending and insightful photographs
  • The War on Water Pollution – Premier Li has just declared war on pollution. Tan expands on the government’s stratagems & offensives and fundamental changes required to shore up the MEP’s arsenal in order to wage a successful war
  • MEP Reform: From Mountaintop to Ocean? – The MEP is currently regarded as too weak to punish polluters due to dispersed authority & overlapping functions. Given the ‘war on pollution’, is reform to make a Super MEP necessary to improve China’s ‘mountains, water, forest, farmland & lakes’?
Tan Qiaoguo
Author: Tan Qiaoguo
Tan Qiaoguo, Ph.D. in Biology, is the Associate Professor of Xiamen University. His research interests include bioaccumulation and toxicity of trace metals in aquatic organisms, process-based models for predicting metal toxicity in organisms and assessment of metal bioavailability in marine sediments. He is the editorial board member of the journal "Environmental Toxicology and Chemistry".
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