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Mercury Pollution & Fertilizers

There may be suspicions that applying fertilizers to soils causes mercury pollution, however, available data indicates that levels of mercury in crop lands are generally safe. No data is available linking fertilizer runoff to mercury pollution in fish, and while mercury pollution has been documented near factories that make fertilizers, washing vegetables decreases the likelihood of ingesting harmful contaminants.

  1. Phosphorus

    • Phosphorus is a necessary component for plant growth. Photosynthesis relies on phosphorus to store and transfer energy. Phosphorus does occur naturally in soils, but it is also processed into fertilizer and applied to crops in combination with nitrogen and potassium in a soluble form that plants can immediately use. It is particularly useful for lettuce and rice crops, both of which have shallow root systems.

    Phosphate Fertilizer Production

    • Phosphate fertilizer is made from phosphate ore, which is mined from deep within the Earth. To make fertilizer, ore is pulverized and treated with sulfuric, nitric or phosphoric acid. The process creates mercury byproducts that reside in minute amounts in fertilizer products. Factory waste products can contain high levels of mercury into the air or water if not treated before disposal. Phosphate fertilizer is a $3.5 billion industry not including the value to worldwide crop production.

    Levels in Soils

    • According to analyses conducted by the EPA using data from areas where fertilizer had been applied across the globe, soil surface concentrations of mercury ranged from non-detectable to .09 mg/kg. However, another study looking specifically at one area near a fertilizer factory found soil levels to be 800 mg/kg.

    Soil Screening Levels

    • The EPA has not developed enforceable criteria for mercury levels in soil, but there is a soil screening guidance document used at Superfund sites to determine what level of a soil contaminant is considered unsafe, requiring remediation. The unsafe level for mercury is considered to be 23 mg/kg if ingested and 10 mg/kg if inhaled. A mercury level of 800 mg/kg would result in limited to no plant growth and could cause significant health defects if ingested or inhaled.

    Other Sources of Mercury

    • The EPA analyses did state that fertilizer was probably not the only source of mercury in soils. Other sources of mercury could come from sewage sludge applications and urban atmospheric deposition, but all sampled levels were well below EPA guidance.

    Mercury Pollution and Fertilizers

    • Mercury in fertilizers results during the manufacturing process from the addition of sulfuric acid. In the United States, special technologies must be implemented to prevent mercury waste from contaminating the environment. Excessive mercury levels in soils can become ingested when vegetables are not washed properly before being eaten. Inhalation can occur when soils are disturbed by farming equipment or with the wind. EPA data indicates that mercury pollution does not occur through the application of phosphate fertilizers on land. However, runoff into nearby rivers and its contribution to mercury accumulations in fish has not been evaluated in depth.

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