Caracterização ultraestrutural das brânquias de Limnoperna fortunei frente à exposição aos biocidas dicloroisocianurato de sódio (NaDCC) e MXD-100

Abstract

Limnoperna fortunei (Dunker 1857), known as the golden mussel, is a bivalve mollusc native to Asia that invaded South America in the 1990s. This species is responsible for ecological and economic damage due to its fouling capacity. Among the methods used to combat it, the biocides MXD-100, composed of tannins and quaternary ammonia, and sodium dichloroisocyanurate (NaDCC), an organic oxidizing compound, are often used to control the infestation in hydraulic systems. This work aimed to characterize the wild L. fortunei gills and to investigate the effects of MXD-100 and sodium dichloroisocyanurate on these structures, by morphological and molecular analyses. At first, the gills were characterized to consolidate the morphological pattern of the structure and then, the animals were exposed to NaDCC (1.5mg/L) and MXD-100 (0.56mg/L) under controlled laboratory conditions, for 24, 48 and 72 hours. Morphological findings in the gill epithelium demonstrated processes related to particle capture and selection, such as highly organized ciliary structures, differentiation between neutral and acidic mucopolysaccharides and abundance of organelles related to high energy demand. Exposure to NaDCC promoted progressive morphological changes and an increase in SOD and HSP70 gene expression during 24 hours, while MXD-100 led to severe morphological changes, in addition to increased expression of SOD, CAT, HSP70, CYP during 24 hours and decrease in CAT enzyme for 48 hours. Thus, NaDCC (1.5 mg/L) showed lethal damage after 72 hours of exposure, requiring continuous exposure to achieve control of the species, while treatment with MXD-100 (5.6 mg/L) showed several effects during the first 24 hours, presenting an acute toxicity in a shorter period of time. Besides to improving the understanding of the biology and structure of the gills of L. Fortunei, this work also allowed us to determine the most efficient periods of action of the most commonly used biocides in fouling control, without extra expenses or eventual waste of these chemicals in nature.