Induction of brown cells in Venerupis philippinarum exposed to benzo(a)pyrene

Sensitivity of histopathological and histochemical parameters in the digestive gland of the apple snail Pomacea canaliculata exposed to cypermethrin

The aim of this study was to evaluate the toxic effects of the pesticide cypermethrin (CYP) in the digestive gland of the apple snail, Pomacea canaliculata, analysing histological and histochemical alterations. Adult snails were exposed to sublethal CYP concentrations (10, 25, and 100 µg/L) under acute (1 day) and sub-chronic (14 days) conditions. Histological analyses of the morphology of the digestive gland were performed and a histopathological condition index (HI) was calculated. Also, both intracellular accumulation of lipofuscins (LF) and neutral lipids (NL) were evaluated. CYP exposure induced tissue damage to this organ, such as disorganisation of the connective tissue, fibrosis, haemocytic infiltration, atrophy, and necrosis under acute and sub-chronic conditions. These alterations, integrated into a single HI value, revealed notable CYP effects during both acute and sub-chronic exposures. Cell type replacement, measured as Vv_BAS, was only observed in the sub-chronic treatment. Under acute conditions, the pyrethroid affected NL accumulation at the highest concentration, while in sub-chronic conditions NL accumulation was only observed at the lowest concentrations. P. canaliculata also showed a dose-dependent response of LF under acute CYP exposure conditions. However, under sub-chronic conditions, this parameter was not sensitive to pesticide exposure. All these relevant structural lesions may affect the normal function of the digestive gland, even though the species presented additional mechanisms, as infiltration of hemocyte and basophilic cell hyperplasia, that help it to tolerate the exposure to pollutants. This study showed that some histological and histochemical parameters are sensitive in P. canaliculata at CYP concentrations to which the snail could be exposed in the environments it inhabits.

Microbiological and Histological Analysis for the Evaluation of Farmed Mussels (Mytilus galloprovincialis) Health Status, in Coastal Areas of Italy

Shellfish farming is a relevant economic activity in Italy. The Gulf of La Spezia is one of the major production areas for mussels: the area is characterized by the presence of numerous human activities that could harm the quality of seawater. Additionally, the presence of potentially pathogenic microorganisms may influence the health status of animals, which must be constantly monitored. To have a clear view of the health conditions of the mussels (Mytilus galloprovincialis) farmed in this area, microbiological, parasitological, and histological analyses were performed. The study was conducted from November 2016 to October 2017. Overall, despite the presence of potentially pathogenic microorganisms for mussels, abnormal mortality rates were not reported during the monitoring period and the histological examination revealed no significant lesions. Our study confirms that studying different aspects together is a useful tool for assessing the health conditions of mussels and points out the importance of adverse environmental conditions for the expression of the pathogenicity of microorganisms.

Effects of elevated CO2 levels on subcellular distribution of trace metals (Cd and Cu) in marine bivalves

Hypercapnia (elevated CO₂ levels) and pollution with trace metals such as Cu and Cd are common stressors in estuarine habitats that can negatively affect physiology and health of marine organisms. Hypercapnia can modulate toxicity of trace metals including Cu and Cd; however, the physiological and cellular mechanisms of the metal-CO₂ interactions are not well understood. We investigated the effects of elevated P_CO2 (∼800 and 2000μatm) and metal exposure (50μgl^-1 of Cu or Cd) on subcellular distribution of metals in two common species of marine bivalves, Eastern oysters Crassostrea virginica and hard shell clams Mercenaria mercenaria. Oysters accumulated higher burdens of Cu and Cd in the gill tissues compared to clams. In both studied species, Cu was predominantly associated with the metabolically active cell compartments (mitochondria, lysosomes, microsomes and cytosolic enzymes), with a modest fraction sequestered by metallothioneins (∼30%) and the insoluble metal-containing granules (MCG) (∼15-20%). Unlike Cu, Cd was largely sequestered by metallothioneins (∼60-70%), with a relatively small fraction associated with the organelles and the cytosolic enzymes. Mitochondria were the main intracellular target for trace metals accumulating higher concentrations of Cd (and in the case of oysters - of Cu) than other organelles or cytosolic enzymes. Cu accumulation in the metabolically active cellular compartments was independent of the CO₂ levels, while Cd content of the organelles and cytosolic enzymes increased at elevated P_CO2 in both studied species indicating that hypercapnia may enhance cellular toxicity of Cd in bivalves. Hypercapnia suppressed the sequestration capacity of metallothioneins for Cu and Cd in oysters but increased Cu and Cd load in clam metallothioneins. Thus, metal-induced metabolic injury in oysters may be exaggerated by hypercapnia which enhances metal accumulation in the potentially sensitive intracellular fractions and suppresses the metal detoxification capacity. In contrast, clams appear to be more resistant to the combined effects of hypercapnia and metal exposure reflecting more efficient and robust detoxification mechanisms of this species.

Elevated gonadal atresia as biomarker of endocrine disruptors: Field and experimental studies using Mytilus trossulus (L.) and 17-alpha ethinylestradiol (EE2)

In the present work we compared the type and frequency of gonadal abnormalities among Mytilus trossulus populations from the Gulf of Gdańsk, Baltic Sea. Observed histopathologies were grouped as regressive changes (RC, gonadal atresia (GA) and regression (GR)), progressive changes (PC, gonadal tumors) and intersex. Sex-based and spatial differences in frequency of RC were found, with the highest frequency of RC and PC found in mussels from polluted station B followed by mussels from station A located near a purification plant outlet. Bivalves from the reference area had the lowest frequency of RC. In order to confirm biomarker applicability of RC, an exposure experiment with model xenoestrogen 17α-ethinylestradiol (EE2) was performed. The exposure of M. trossulus to 50 and 500ngdL^-1 of EE2 resulted in an increased frequency of gonadal regression and atresia, including melanized hemocytes infiltration in seminiferous tubules. We thus suggest that these changes can serve as biomarkers of endocrine disrupting compounds in biomonitoring studies.

Toxicity assessment of ZnO-decorated Au nanoparticles in the Mediterranean clam Ruditapes decussatus

The synthesis of hybrid nanomaterials has greatly increased in recent years due to their special physical and chemical properties. However, information regarding the environmental toxicity associated with these chemicals is limited, in particular in the aquatic environment. In the present study, an experiment was performed in which the marine bivalve (Ruditapes decussatus) was exposed for 14days to 2 concentrations of zinc oxide-decorated Au nanoparticles (Au-ZnONPs: Au-ZnONP50=50μg/L; Au-ZnONP100=100μg/L). The stability and resistance of Au-ZnONPs in the natural seawater were assessed by combining transmission electron microscopy and dynamic light scattering. Inductively coupled plasma-atomic emission spectroscopy revealed uptake of these nanoparticles within clams and their ability to induce metallic deregulation. The results obtained indicate that Au-ZnONPs induce biochemical and histological alterations within either the digestive gland or gill tissues at high concentration. This was deduced from the significant increase in H₂O₂ level, superoxide dismutase and catalase activities and malondialdehyde content. Furthermore, the toxicity of Au-ZnO nanoparticles was linked with the increase of intracellular iron and calcium levels in both tissues. Histological alterations in gill and digestive gland were more pronounced with Au-ZnONP100 and this is likely related to oxidative mechanisms. Gill and digestive gland are differentially sensitive to Au-ZnONPs if the exposure concentration is higher than 50μg/L. In conclusion, the parameters considered here could constitute reliable biomarkers for evaluation of hybrid nanoparticles toxicity in environmental model organisms. In addition, based on the results obtained, gill and digestive gland of R. decussatus could be proposed as models to detect harmful effects of hybrid nanoparticles.

Contaminant-induced oxidative stress in fish: a mechanistic approach

The presence of reactive oxygen species (ROS) in living organisms was described more than 60 years ago and virtually immediately it was suggested that ROS were involved in various pathological processes and aging. The state when ROS generation exceeds elimination leading to an increased steady-state ROS level has been called "oxidative stress." Although ROS association with many pathological states in animals is well established, the question of ROS responsibility for the development of these states is still open. Fish represent the largest group of vertebrates and they inhabit a broad range of ecosystems where they are subjected to many different aquatic contaminants. In many cases, the deleterious effects of contaminants have been connected to induction of oxidative stress. Therefore, deciphering of molecular mechanisms leading to such contaminant effects and organisms' response may let prevent or minimize deleterious impacts of oxidative stress. This review describes general aspects of ROS homeostasis, in particular highlighting its basic aspects, modification of cellular constituents, operation of defense systems and ROS-based signaling with an emphasis on fish systems. A brief introduction to oxidative stress theory is accompanied by the description of a recently developed classification system for oxidative stress based on its intensity and time course. Specific information on contaminant-induced oxidative stress in fish is covered in sections devoted to such pollutants as metal ions (particularly iron, copper, chromium, mercury, arsenic, nickel, etc.), pesticides (insecticides, herbicides, and fungicides) and oil with accompanying pollutants. In the last section, certain problems and perspectives in studies of oxidative stress in fish are described.