Impacts of hazardous air pollutants emitted from phosphate fertilizer production plants on their ambient concentration levels in the Tampa Bay area

Abstract

The concentrations and distribution of hazardous air pollutants (HAPs) metals emitted from four phosphate fertilizer plants in Central Florida, as well as their environmental and health impacts, were investigated. It was hypothesized that the modern control devices employed in the plants would lower the exposure, if any, to an acceptable level. The dominant HAP metals emitted from the stacks of these plants were identified to be Mn, Cr, Ni, and Se. The ambient concentrations at six receptors (Zephyrhills, Plant City, Tampa, Lakeland, Tower Dairy, and Sydney) downwind the plants estimated by AERMOD revealed the maximum ground level concentrations were lower than the European Communities and USEPA standards. Source apportionment estimated by the chemical mass balance (CMB) model indicated that marine (45.5 ± 17.1 %) and geological (17.3 ± 10.6 %) were the top two contributors for 26 elements, while the phosphate fertilizer plants contributed only 1.14 ± 0.55 %. Unexpectedly, the maximum ground-level risks for Cr from plant A (1.3 × 10⁻⁶ ± 8.4 × 10⁻⁸) and plant D (1.1 × 10⁻⁶ ± 6.7 × 10⁻⁸) were slightly higher than the general guideline of 1 × 10⁻⁶, but they occurred within the facility limit. No other metals approached levels of concern for non-cancer risks. One possible source for Cr emissions from these plants may be stainless steel milling balls used in the production process. Sensitivity analysis of the meteorological data in 2001–2005 showed only 7.7 % variation in the corresponding risk. Overall, phosphate fertilizer plants make minor contribution to the ambient levels of HAP metals compared to other sources for the general population in the Tampa Bay area, although more in-depth investigation into the Cr emissions is recommended.