Fluorosis in a Wild Cotton Rat (Sigmodon hispidus) Population Inhabiting a Petrochemical Waste Site

Abstract

We have developed an in situ mammalian model for evaluating environmental contamination using wild cotton rats. In a series of experiments, 200 male cotton rats were captured during 4 collection periods (spring 1991 = 35; fall 1991 = 60; spring 1992 = 53; fall 1992 = 52). A total of 103 of these cotton rats were captured from control sites, and the remaining 97 were captured from an abandoned oil refinery. All sites were located in the vicinity of Cyril, Oklahoma. There were alterations in the incisors of cotton rats captured from the refinery site. Normal color of cotton rat incisors is deep yellow-orange, which is imparted by a pigment normally produced by ameloblasts. Grossly, the upper incisors of 37 of 97 rats and lower incisors of 54 of 97 rats were affected. The affected incisors were white, chalky, and thin with striations and erosions of the enamel. Microscopic examination revealed that there were dysplastic and necrotic changes in the ameloblasts. The bone fluoride levels were significantly higher in rats captured from the refinery as compared to the rats captured from the control sites.

Fluorosis Risks to Resident Hispid Cotton Rats on Land-Treatment Facilities for Petrochemical Wastes

“…Less than 1% of cotton rats from reference sites showed any sign of fluorosis and those that did had mild dental lesions. Taken alone, this indicates that cotton rats are a good in situ biomonitor for fluoride contamination at the levels experienced on the three land-treatment sites in this study and concurs with previous studies (Paranjpe et al, 1994).…”

“…Few studies have attempted to document consequences of exposure to excessive levels of fluoride in soil for wild rodent communities. Exceptions include reports of Paranjpe et al (1994) for cotton rats residing on petroleum waste sites and Boulton et al (1994a) for field voles and bank voles re-FIGURE 1. Mean (ϮSE) severity scores of dental fluorosis for incisors (0-5) and concentrations of contaminants in bone (mg/kg) of adult cotton rats collected from land-treatment sites (n ϭ 3) and matchedreference sites (n ϭ 3) in Oklahoma.…”

“…For example, Boulton et al (1994a) reported dental lesions in field voles (Microtus agrestis) and bank voles (Clethrionomys glareolus) in association with environmental exposure to contaminated soils around aluminum smelters, fluorochemical industrial works, and mine tailings. A high incidence of dental lesions consistent with dental fluorosis has been reported in cotton rats (Sigmodon hispidus) on petroleum waste sites (Paranjpe et al, 1994).…”

“…Over 50% of the hazardous wastes generated by the petroleum industry have been disposed of through land-treatment operations (American Petroleum Institute, 1984), yet no comprehensive assessment of their impact on terrestrial ecosystems has been completed. Initial surveys by Paranjpe et al (1994) and McMurry (1993) suggested that fluoride toxicity risks might be high for land-treatment sites. New techniques to monitor environmental contamination that are biologically based have the potential to identify unknown problems.…”

Cadmium-Induced Dental Lesions in Ovariectomized Rats

“…Discoloration of teeth has been reported with fluorosis in human beings (8), domestic animals (19), and wild cotton rats (20). Experimentally, brown and white striations or discolorations with mottling are observed in the incisor of rats treated with fluoride (17).…”