Immunotoxicity risks associated with land-treatment of petrochemical wastes revealed using an in situ rodent model

Land-treatment of petrochemical wastes is a widely used method to dispose o f hazardous and non-hazardous waste by biodegradation. However, no comprehe nsive assessment of the impact of such disposal techniques on terrestrial e cosystems has been conducted. Despite the presence of suspected immunotoxic ants in the soil, wild rodents frequently reside on these waste sites after closure or abandonment. We explored the seasonal sensitivity of the immune system of the hispid cotton rat (Sigmodon hispidus) to in situ exposures o n sites land-treated with petrochemical wastes. Animals were monitored on f ive contaminated land-treatment sites and five ecologically matched-referen ce sites in Oklahoma, USA, over two seasons (summer and winter). Most hemat ological parameters were not adversely affected by land-treatment; however, platelet counts were 26% greater in cotton rats from land-treatment sites compared to reference sites in winter. Significant treatment-related differ ences were observed in total serum protein concentrations, organ mass and o rgan cellularity, but these differences were not consistent across the five land-treatment units. Lymphoproliferative responses of cotton rat splenocy tes stimulated in vitro were elevated for a T-cell mitogen and depressed fo r a B-cell mitogen in animals from land-treatment compared to reference sit es. The ability of splenocytes to proliferate in response to interleukin-2 receptor-binding was not influenced by treatment. Total yields of peritonea l cells, yield of peritoneal macrophages, and yield of peritoneal lymphocyt es were influenced to varying degrees by land-treatment. Functionally, in v itro metabolic activity of peritoneal macrophages was 114% greater in cotto n rats from land-treatment sites compared to reference sites during summer. These results indicate that petrochemical wastes applied to soils on these five land-treatment sites had variable immunomodulatory effects in residen t cotton rats. Immune alterations for some assays were indicative of enhanc ement on some land-treatment sites while suppressive on other land-treatmen t sites, which could have been a function of type and concentration of immu notoxicants present on each site and highlights the uniqueness of each land -treatment site. (C) 2001 Elsevier Science Ltd. All rights reserved.