Killer let loose

Arsenic and lead leach out from popular US fertiliser

Last Updated: Saturday 04 July 2015

ironite, a widely used fertiliser in the us, releases enough of lead and arsenic in standard leaching tests to be classified as a hazardous waste. Moreover, its heavy metals are 'bioavailable', implying they can be absorbed by lifeforms. These are the findings of a study conducted by Bradjesh Dubey and Timothy Townsend of the University of Florida, usa. The researchers found that the fertiliser is extremely acidic, and hence its leaching in water results in high lead and arsenic concentrations in the 'leachate' (water).

Ironite is produced from the tailings of a former mine located in Humboldt, Arizona. The fertiliser -- a mixture of mine tailings, sulfuric acid and urea -- is popular with the gardeners of the country because the iron in the mine tailings greens up lawns without promoting heavy growth. A federal exemption allows manufacturers to list only nutrients on the labels of the products. As a result, gardeners using Ironite are not informed about its potentially hazardous ingredients.

Previous studies have highlighted Ironite's exceedingly high concentrations of heavy metals -- up to 3,600 milligrammes (mg) of arsenic per kilogramme (kg) of fertiliser and up to 2,900 mg of lead per kg of fertiliser.

Ironite's Arizona-based manufacturer, Ironite Products Corporation, maintains its products are safe. A technical report commissioned by the company indicates that these metals are present in the fertiliser as the minerals galena and arsenopyrite, which are said to be very stable in the environs.

But Dubey and Townsend refute this claim. "Our results show that when Ironite is applied in the commonly found acidic conditions, the heavy metals do leach out. Moreover, the lead and arsenic is bioavailable if the Ironite is consumed by a child," says Townsend. Their results provide crucial evidence for an ongoing risk assessment by the us Environmental Protection Agency, which could lead to a nationwide ban on such products.

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