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Daily Archives: November 2, 2008

Pesticide, fertilisers linked to decline of amphibians

by Marlowe Hood

A pesticide compound commonly used in the United States is linked to the growth of tiny parasites that sicken and kill frogs and also harms the amphibians' immune defences against infection, according to a study published this week.
The impact of this chemical is boosted in the wild by phosphate fertilisers, the investigators believe.
Runoff from fertilisers into ponds encourages the proliferation of snails that are a natural host to the flatworm parasites, they say.
The flatworms, called trematodes, are notorious for causing limb malformations, kidney damage and sometimes death in several species of frog.
The new study points the finger at atrazine, an active ingredient in several herbicide products manufactured by a Swiss-based company, Syngenta.
Atrazine was banned in the European Union in 2004 after the chemical showed up in drinking water, but has over the last 15 years become a leading farm chemical in the United States, especially in corn-growing regions.
In a field survey led by Jason Rohr of the University of South Florida, scientists measured more than 240 variables in 18 Minnesota wetlands that could account for the rate at which frogs are infected by trematodes.
The strongest link by far was with atrazine concentrations, which accounted for more than 50 percent of the likelihood that the amphibians would become diseased.
When the presence of atrazine was combined with traces of phosphate fertilizer — runoff from nearby agricultural plots — the rate of diseased frogs went up to 75 percent.
Seeking to find out more, the researchers raised tadpoles for four weeks in several 290-gallon (1,100-litre) tanks containing snails, leaves and insect larvae, to approximate a natural environment.
In tanks where atrazine was added in concentrations found in wetlands, four times as many snails grew compared with the population that was in water free of the herbicide. The population of the parasitic flatworms exploded too.
Green frogs used in the experiment showed significantly higher levels of trematode infection, while pickerel frogs experienced high rates of mortality.
"The wetlands survey was highly suggestive that atrazine was causing the increase in larval trematode load," Rohr told AFP by phone.
"The follow-up experiment really demonstrated that it was indeed a causal link."
He cautioned, though, that these findings did not by themselves explain a massive slump in American frog populations, a fall that began in the mid-1990s and is mirrored by shrinking populations of amphibians elsewhere in the world.
Global warming, inflicting a loss of wetland habitat, has been blamed as one of the causes.
Syngenta, asked to reply by AFP, said in a statement: "50 years of use and a vast amount of research has shown that (atrazine) can be used safely with no long-term detriment to ecosystems."
The concentrations of the chemical in wetlands reported in the Rohr study were well below the "level of concern" thresholds established by the US Environmental Protection Agency (EPA), it noted.
Rohr added that there could be other chemicals in addition to atrazine and fertilizers that affected disease risk.
"Many chemicals can be immuno-suppressive, and standard toxicity tests used to register chemicals in the United States and Europe are conducted on isolated individuals, ignoring interactions with other species, such as their parasites.
"Thus, our findings are likely the tip of the iceberg for pollution-induced disease emergence in both humans and wildlife."
The study was published on Thursday in the London-based journal Nature.
Rohr said that a senior biologist from the EPA, Thomas Steeger, had requested a copy of the study.
In its latest evaluation of atrazine, the EPA concluded in 2006 that the product posed no threat to human health.


‘The Great Wall is still tiny’

"In a zone with less than three months of rains you cannot expect spectacular results. These gum trees do not need extra water, they develop their extensive root system first and grow taller very slowly," said Lieutenant Almamy Diarra of the water and forest service.
"These are trees that support drought very well — in the dry season they shed their leaves to prevent the loss of water," he said.
The trees are also very well suited to stopping desertification. Their roots "fix the soil layers and facilitate water infiltration and this creates a microclimate that allows other plants to settle in the same area," he said.
Statistics in hand, another department official, Souleymane Ndoye, said they replanted 300 hectares (740 acres) in 2005, 400 in 2006 and 675 last year.
"This year the goal was to have 5,000 hectares reforested. With God's help we planted 5,230," he said.
"At the moment Senegal does not have the financial means to finish its part of the wall, Diarra explained.
"The Great Wall is still tiny," he conceded.
"We need to plant 25,000 hectares every year for at least 25 years. All the rural communities have to work on it at the same time."
The wall project has provided jobs for the village's young men in the tree nursery, said Kadio Ka, the female chief of the village and a mother-of-eight.
"The majority of the people here raise livestock and harvest gum from the gum trees," she said.
"When those gum trees mature the whole village will profit from them."
But ranger Ndoye warns that the villagers will have to be patient.
"Reforestation over a 543-kilometre area in Senegal will take several generations," he added.