Accumulation of Lead in Soil from Waste-derived Commercial Fertilizer Eden Mann Abstract Non-nutritive metals from industrial waste are recycled into fertilizer as a cheap method of disposal. Soil naturally contains traces of heavy metals; however, the repetitive application of fertilizers containing these heavy metals may result in accumulation of lead to levels that may have toxic consequences for all life forms. This study estimates and compares accumulation of lead in agricultural soils from waste-derived commercial fertilizers under new California regulations by calculating the time it will take to reach USEPA standards for hazardous concentrations of lead under different worst-case scenarios and also for specific real-life crop examples. Grain, root, and vegetable crops were compared in the worst-case scenarios. Fertilizer usage was based on high-end phosphate nutrient requirements for each of the categories. Tillage depth and soil densities were specific to California soils. It was assumed the maximum allowable concentration of lead under the new California regulations was present in the fertilizer. The specific crop examples in various California counties were compared: bell pepper in Kern, onions in Riverside, and grapes in Napa. Variables such as fertilizer use and tillage depth were specific to local growing practices; soil density was specific to the location of the crop. The results show that lead poses a negligible risk of accumulating to toxic concentrations within the next 100 years under the worst-case scenarios and the specific crop scenarios. Therefore, new California standards for lead in fertilizers may be adequate; however, states without regulations may want to set standards for lead in fertilizer to prevent rapid accumulation to hazardous levels.Introduction A commercial fertilizer is “a substance containing one or more recognized plant nutrients that is used for its plant nutrient content or is designated for use or claimed to have value in promoting plant growth” (WSDA 2003). Primary nutrients are defined as nitrogen, phosphorus, and potassium. Secondary nutrients include calcium, magnesium, and sulfur (WSDA 2003). Micronutrients are defined as boron, manganese, chlorine, molybdenum, cobalt, sodium, copper, zinc, and iron (WSDA 2003). Recently, however, non-nutritive substances including lead, mercury, arsenic, cadmium, chromium, and dioxin have been recycled into some fertilizers as a cheaper alternative to proper disposal (USEPA 1999, Environmental Working Group 1998, The Fertilizer Institute 2000, WSDA 2001). This practice is occurring all over the world. Toxic waste from cement kiln dust, pulp mills, mining, incinerated medical supplies, spent battery acid, contaminated industrial phosphoric and sulfuric acid, and the aluminum industry is sent to fertilizer companies where it is then rolled into fertilizer pellets if it contains primary or secondary nutrients such as zinc, nitrogen, or phosphorus (USEPA 1999, Environmental Working Group 1998, The Fertilizer Institute 2000, WSDA 2001). A total of 454 companies identified as fertilizer manufacturers and farms in the Toxic Release Inventory received 271 million pounds of toxic waste containing 69 types of toxics and 6.2 million pounds of lead compounds in a five-year period (Environmental Working Group 1998). There are economic incentives for both the waste providing industries and fertilizer manufactures—it is cheap for industries to dispose of their hazardous waste in this fashion and benefits fertilizer manufacturers because they receive free or discounted nutrients (Environmental Working Group 1998). Although the United States Environmental Protection Agency (USEPA) admits that “no specific regulations exist requiring fertilizer producers to list non-nutritive constituents on fertilizer labels, so it is difficult to quickly ascertain the levels of heavy metals (and other chemicals) in fertilizers” and “chemicals such as radionuclides and persistent organics (e.g., chlorinated dibenzodioxins/furans) are in this category,” they claim that there is no specific evidence showing that the heavy metals recycled into fertilizers pose a threat to human health (USEPA 1999). In 2002, the California State Department of Agriculture implemented new regulations which establish maximum concentration limits of arsenic, cadmium, and lead in fertilizer that vary depending upon the concentrations of specified nutritive constituents (i.e. iron, zinc, andmanganese for mineral products and phosphate for commercial fertilizers) in the fertilizer (CDFA 2001). The higher the concentration of “nutrients,” the more “non-nutritive” metals the California State Department of Agriculture allows (CDFA 2001). This means root crops, which require more phosphate than grain crops will receive a larger quantity of arsenic, cadmium and lead. Many studies conclude that ingestion of crops contaminated with cadmium from waste-derived fertilizers, as opposed to other methods of exposure, is the biggest risk posed to humans (CDFA 1998, The Fertilizer Institute 2000, Kuo et. al. 1999). These studies, however, neglect the ecological impacts and long-term impacts of heavy metal accumulation in soil due to fertilizer application. While cadmium may be taken up into plants, arsenic and lead remain in the soil where they may accumulate rapidly with persistent fertilizer application (CDFA 1998, USEPA 1999a). Lead exposure from dermal absorption, inhalation, or ingestion of crops and soil, can target the nervous system of humans and animals and may result in toxicity or death (ASTDR 1997). Children are more likely to directly ingest contaminated soil than adults; even low levels of lead may cause developmental problems, poor academic performance, lowered IQ, juvenile delinquency, and neurological damage (Hamel et. al. 2003). According to USEPA Administrator Carol Browner, “lead poisoning continues to be one of the most serious environmental threats to children in this country” (USEPA 2000). New California standards for non-nutrient metals in fertilizer do not anticipate long-term health risks from exposure and environmental impacts that may become more likely as pollutant concentrations increase. The standards for non-nutrient metals in fertilizer fail to consider the health risks or environmental impacts of long-term heavy metal accumulation in the soil. The longest study of heavy metal
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