In October 2001 and March 2002, a field survey of central stonerollers (Campostoma anomalum) from
perchlorate-contaminated streams in central Texas was conducted to assess thyroid endocrine disruption. A survey of adult male and female cricket frogs (Acris crepitans) was performed at the same site between 2001 and 2003.
Perchlorate is an oxidizer primarily used in solid-fuel rockets, and many sites that processed or used
perchlorate are now contaminated. Histological analysis revealed that the fish from contaminated sites had increased thyroid follicular
hyperplasia,
hypertrophy, and
colloid depletion. Multivariate analysis was generally found to be more powerful than univariate analysis. Seasonal differences existed in the degree of thyroidal perturbation were discovered, and fish were generally less sensitive to thyroidal perturbations in March compared to October. Thyroidal histological indicators were also correlated to levels of
perchlorate in the fish, water, and periphyton. Periphyton was frequently most strongly correlated to thyroidal indices, suggesting that exposure through the food chain may be of import. In addition, one of the presumed reference sites turned out to be contaminated with
perchlorate, and this was reflected by thyroidal
biomarkers before
perchlorate was detected in the stream water or biota. There was no evidence of
colloid depletion or
hyperplasia in frogs from any of the sites, although frogs from two sites with greatest mean water
perchlorate concentrations exhibited significantly greater follicle cell
hypertrophy. Furthermore, there was a significant positive correlation between follicle cell height and mean water
perchlorate concentrations for frogs collected from all sites. This is the first known published account of
perchlorate-induced thyroid disruption in fish under field situations, only the second known published account for amphibians, and also points out the value of
biomarkers for contaminant biomonitoring.