Exposure to Perchlorate Induces the Formation of Macrophage Aggregates in the Trunk Kidney of Zebrafish and Mosquitofish

—Environmental contamination of ground and surface waters by perchlorate, derived from ammonium perchlorate (AP) and other perchlorate salts, is of increasing concern. Exposure to perchlorate can impair the thyroid endocrine system, which is thought to modulate renal and immune function in vertebrates. This study with zebrafish Danio rerio and eastern mosquitofish Gambusia holbrooki examined the histological effects of perchlorate on the trunk kidney, which in teleosts serves excretory and hemopoietic functions and therefore may be a target of perchlorate effects. Adult zebrafish of both sexes were exposed in the laboratory to waterborne, AP-derived perchlorate at measured concentrations of 18 mg/L for 8 weeks. Adult male mosquitofish were exposed to waterborne sodium perchlorate at measured perchlorate concentrations of 1–92 mg/L for 8 weeks. Control fish were kept in untreated water. The region of the body cavity containing the trunk kidney was processed from each fish for histological analysis. Macrophage aggregates (MAs), possible markers of contaminant exposure or immunotoxic effect, were present in the hemopoietic region of the kidney in both species exposed to perchlorate. The estimated percent area of kidney sections occupied by MAs was greater in zebrafish exposed to perchlorate at 18 mg/L (P , 0.05) than in controls. In male mosquitofish, the incidence of renal MAs increased proportionally with sodium perchlorate concentration and was significantly different from that of controls at 92 mg/L (P , 0.05). These observations confirm that in fish the kidney is affected by exposure to perchlorate. The concentrations of perchlorate at which the effects were noted are relatively high but within the range reported in some contaminated habitats. Ammonium perchlorate (AP) is a strong oxidant used primarily as a rocket propellant in military and aerospace industries and operations (Fisher et al. 2000). After the dissociation of AP into ammonium and perchlorate ions in water, the resulting perchlorate anion persists in the environment for many years (Fisher et al. 2000; Urbansky 2002). Environmental contamination of ground and surface waters by perchlorate derived from AP and other perchlorate salts is of increasing concern (Urbansky 2002). * Corresponding author: [email protected] 1 Present address: School of Natural Resources, Ohio State University, Columbus, Ohio 43210, USA. Received April 18, 2004; accepted June 6, 2004 The best known biological impact of perchlorate in animals is the impairment of thyroid gland function. Perchlorate alters thyroid function by competitively blocking iodide influx at the sodium iodide symporters that regulate the amount of iodide transported into thyroid follicles. Because iodide is necessary for thyroid hormone production, this blocking reduces the levels of thyroid hormones in blood (Wolff 1998). As a result, the pituitary gland increases its production of thyroid-stimulating hormone (TSH) in an attempt to restore thyroid hormone levels. Prolonged exposure to perchlorate causes hyperstimulation of the thyroid gland (Wolff 1998; Soldin et al. 2001). For example, histopathological studies with several vertebrate species have revealed that exposure to APD ow nl oa de d by [ SU N Y B ro ck po rt ] at 1 2: 03 1 9 D ec em be r 20 11