Histopathology as an Approach to Evaluate the Effect of an Oil Spill on Fishes of the Arroio Saldanha and Rio Iguaçu (Brazil)

Abstract

ABSTRACT In July of 2000, an accident occurred at the Presidente Getúlio Vargas Refinery (REPAR), located in the Municipality of Araucaria, Southern Brazil which involved the spilling of about 4 million liters (25,160 barrels) of crude oil. This was considered the largest oil spill in the history of Brazil. Despite of the use of containment barriers, the oil slick reached a small creek (Arroio Saldanha) and, further downstream, two important rivers in the region (Rio Barigüi and Rio Iguaçu). In this stretch, the Rio Iguaçu and the Rio Barigui are highly polluted, having crossed Curitiba, a city that has 2+ million inhabitants, and several industrial areas. The histopathological study of the gills and liver of 2 species of fishes was used to evaluate the impact of the oil on the fish fauna in the affected rivers. The choice of fish species reflects their year-around availability and their predicted roles in the ecosystem. Astyanax sp. is mainly pelagic and Corydoras paleatus is demersal; these fish species should, therefore, indicate the environmental health of these two compartments of the streams. The spatial and temporal distribution of histological alterations was analyzed from up to 10 specimens of each species of fish from collections made in 5 sites. A relative impact index (Ri) was determined by assigning a weight to the extent of each pathology observed in sections of each organ/fish (ii = 1 or 2, for moderate or severe pathologies, respectively). The Ri of each organ and fish specimen was calculated as the average impact of the observed histological injuries using the formula: Ri = Σii/n. Variations of the gill and liver Ri suggest a relative regeneration of the environmental health of the impacted streams. A better understanding of the impact caused to the aquatic system by the oil spill is greatly hindered by the presence of other persistent or sporadic events of environmental aggression to which these streams are submitted.