Ecotoxicological risks associated with land treatment of petrochemical wastes. I. Residual soil contamination and bioaccumulation by cotton rats (Sigmodon hispidus)

Petrochemical waste contains both organic and inorganic contaminants that can pollute soil and may pose significant ecological risks to wildlife. Petrochemical waste typically is disposed of in land treatment units, which are widespread throughout Oklahoma and the United States. Few studies have been conducted evaluating possible toxicity risks to terrestrial organisms residing on these units. In this study, the extent of soil contamination with fluoride (F), metals, and organic hydrocarbons, the bioaccumulation of F and metals in cotton rats (Sigmodon hispidus), the relationship between contaminants in soil and in tissues of cotton rats, and the level of potentially toxic polycyclic aromatic hydrocarbons (PAHs) in soil were determined on land treatment units. Over a 2-yr period, cotton rats and soils were collected and analyzed from 5 land treatment and matched reference units. The number of land treatment units with soil metal contamination (in parentheses) included: Cr, Cu, Pb (5); Al, As, Ni, Sr, Zn (4); Ba (3); and Cd, V (2). The number of land treatment units with soil PAH contamination (in parentheses) were naphthalene, phenanthrene, benzo[g,h,i]perylene (3); acenaphthene, anthracene, pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[a]pyrene, indeno[1,2,3-c,d]pyrene, dibenz[a,h]anthracene (2); and acenaphthylene, fluorene, fluoranthene, benzo[k]fluoranthene (1). Total PAH and total petroleum hydrocarbons (TPH) were elevated at all five land treatment units. Mean sums of benzo[a]pyrene (BaP) equivalents (BaP_equiv) were not affected on land treatment units as compared to reference units. Units 1 and 3 were significantly higher in levels of metals, total PAH, TPH, and BaP_equiv than the other units. Pb and F bioaccumulated in bone and Pb bioaccumulated in kidney of cotton rats. F in bone of 496 to 2212 mg/kg was 3- to 15-fold greater than mean F in bone of cotton rats from reference units. Elevated levels of Pb in bone of 4.6 to 24.8 mg/kg were 460- to 2500-fold greater than mean Pb in bone of cotton rats from reference units. Elevated levels of Ph in kidney of 0.31 to 1.08 mg/kg were 10- to 36-fold greater than mean Pb in kidney of cotton rats from reference units. Bone F was an accurate predictor of the severity of dental fluorosis. Strong relationships were found between bone F and HCl-extractable F and bone F and total F in soils of land-treatment units. A strong relationship was discovered between Pb in bone and Pb in soil. Land treatment appears to have been effective as a remediation technology in reducing levels of individual PAHs and the sum of BaP equivalents to background levels on units 2, 4, and 5 but not on units 1 and 3. This study shows that certain contaminants such as Pb and F tend to bioaccumulate in cotton rats collected from land treatment units. Land treatment was ineffective in reducing levels of these contaminants to background levels that will not pose an increase in risk to terrestrial mammals. Therefore, to avoid accumulation of these contaminants in cotton rats and their possible deleterious effects, these contaminants should be measured, and land application rates of petrochemical waste should be managed to avoid excessive loading into soil systems.