Boron is naturally released to soil and water by rainfall, weathering of boron-containing minerals, desorption from clays and by decomposition of boron-containing organic matter. Man-made sources include application of boron-containing fertilizers or herbicides, application of fly ash or sewage sludge as a soil amendment, the use of waste water for irrigation or land disposal of boron-containing industrial wastes (Butterwick et al. 1989; Hollis et al. 1988; Mumma et al. 1984; Nolte 1988; Rope et al. 1988).
No quantitative data were located regarding man-made releases of boron compounds to soil. However, Mumma et al. (1984) reported that the boron concentration in sewage sludges from 23 U.S. cities ranged from 7.1 to 53.3 mg/kg. Landfilling or land application is a common disposal method for these sludges.
Data from the CLP Statistical Database indicate boron was detected in soil at about 5% of hazardous waste sites at a geometric mean concentration of 8,055 ppm in positive samples (CLPSD 1989). However, earlier data from the CLPSD (1980-1983) indicate a geometric mean concentration of boron of 21 mg/kg and a maximum concentration of 320 mg/kg (Eckel and Langley 1988), essentially equivalent to reported background levels of boron in soil. Clarification of the discrepancy in the data is necessary in order to compare boron levels at hazardous waste sites to background levels.
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