Several Palaeozoic mass extinction events during the Ordovician and Silurian periods (ca. 485 to 420 to million years ago) shaped the evolution of life on our planet. Although some of these short-lived, periodic events were responsible for eradication of up to 85% of marine species, the exact kill-mechanism responsible for these crises remains poorly understood.
An international team led by Thijs Vandenbroucke (researcher at the French CNRS and invited professor at UGent) and Poul Emsbo (US Geological Survey) initiated a study to investigate a little known association between 'teratological' or 'malformed' fossil plankton assemblages coincident with the initial stages of these extinction events.
In a paper just published in Nature Communications, they present evidence that malformed fossil remains of marine plankton from the late Silurian (415 million years ago) contain highly elevated concentrations of heavy metals, such as iron, lead, and arsenic. These are well-known toxins that cause morphologic abnormalities in modern aquatic organisms; which led the authors to conclude that metal poisoning caused the malformation observed in these ancient organisms and may have contributed to their extinction and that of many other species.
More than 8 million acres of China's farmland is too polluted with heavy metals and other chemicals to use for growing food, a Cabinet official said Monday, highlighting a problem that is causing growing public concern.
The threat from pollution to China's food supply has been overshadowed by public alarm at smog and water contamination but is gaining attention following scandals over tainted rice and other crops. The government triggered complaints in February when it refused to release results of a nationwide survey of soil pollution, declaring them a state secret.
The figure given at a news conference by Wang Shiyuan, a deputy minister of the Ministry of Land and Resources, would be about 2 percent of China's 337 million acres of arable land.
Some scientists have given higher estimates of as much as 60 million acres, or one-fifth of the total, though it is unclear how much of that would be too badly contaminated for farming.
The issue poses a dilemma for communist leaders who want to maximize food production but face public pressure to ensure safety after an avalanche of scandals over shoddy infant formula and other goods.
The explosive growth of Chinese industry, overuse of farm chemicals and lax environmental enforcement have left swathes of the countryside tainted by lead, cadmium, pesticides and other toxins.
Investigations by the Ministry of Environmental Protection have found "moderate to severe pollution" on 3.3 million hectares (8.3 million acres), Wang said at a news conference.
"These areas cannot continue farming," Wang said. He did not say whether the information came from the national pollution survey.
Farmers already are prohibited from raising crops for human consumption in areas across China that are deemed too badly polluted. But tainted rice and other crops have made their way into the food supply.
