Effects of cadmium exposure on embryogenesis of Stagnicola elodes (Mollusca, Gastropoda): potential consequences for parasite transmission

Parasites and pollution: the effectiveness of tiny organisms in assessing the quality of aquatic ecosystems, with a focus on Africa

The aquatic environment represents the final repository for many human-generated pollutants associated with anthropogenic activities. The quality of natural freshwater systems is easily disrupted by the introduction of pollutants from urban, industrial and agricultural processes. To assess the extent of chemical perturbation and associated environmental degradation, physico-chemical parameters have been monitored in conjunction with biota in numerous biological monitoring protocols. Most studies incorporating organisms into such approaches have focussed on fish and macroinvertebrates. More recently, interest in the ecology of parasites in relation to environmental monitoring has indicated that these organisms are sensitive towards the quality of the macroenvironment. Variable responses towards exposure to pollution have been identified at the population and component community level of a number of parasites. Furthermore, such responses have been found to differ with the type of pollutant and the lifestyle of the parasite. Generally, endoparasite infection levels have been shown to become elevated in relation to poorer water quality conditions, while ectoparasites are more sensitive, and exposure to contaminated environments resulted in a decline in ectoparasite infections. Furthermore, endoparasites have been found to be suitable accumulation indicators for monitoring levels of several trace elements and metals in the environment. The ability of these organisms to accumulate metals has further been observed to be of benefit to the host, resulting in decreased somatic metal levels in infected hosts. These trends have similarly been found for host-parasite models in African freshwater environments, but such analyses are comparatively sparse compared to other countries. Recently, studies on diplozoids from two freshwater systems have indicated that exposure to poorer water quality resulted in decreased infections. In the Vaal River, the poor water quality resulted in the extinction of the parasite from a site below the Vaal River Barrage. Laboratory exposures have further indicated that oncomiracidia of Paradiplozoon ichthyoxanthon are sensitive to exposure to dissolved aluminium. Overall, parasites from African freshwater and marine ecosystems have merit as effect and accumulation indicators; however, more research is required to detail the effects of exposure on sensitive biological processes within these organisms.

Parasitological Analysis and Gill Histopathology of Pearl Dace (Semotilus Margarita) and Brook Stickleback (Culaea Inconstans) Collected from the Athabasca Oil Sands Area (Canada)

Pearl dace (Semotilus margarita) and brook stickleback (Culaea inconstans) were collected from tributaries of the Athabasca River (Alberta, Canada), upstream (reference site) and downstream of oil sands deposits where fish were expected to be exposed to naturally occurring oil sands constituents. The objective was to determine if fish collected from these sites exhibited differences in the prevalence or intensity of infection by parasites or in gill histology. Dace did not display significant differences in these parameters. Alternately, upstream stickleback were predominantly infected by complex life history parasites, while downstream fish were primarily infected by parasites with simpler life histories. Moreover, downstream stickleback exhibited significantly more clubbing and aneurysms in secondary gill lamellae relative to upstream fish. This suggested a difference in habitat quality between upstream and downstream sites. However, based on basic body condition parameters of the fish, it would appear that any impacts upon the health of the fish due to the presence of naturally occurring oil sands associated chemical constituents would have been minor.

Diversity of metazoan parasites of the Mozambique tilapia, Oreochromis mossambicus (Peters, 1852), as indicators of pollution in the Limpopo and Olifants River systems

Aquatic systems are affected by a variety of anthropogenic activities that decrease water quality through the introduction of organic and inorganic pollutants. To investigate the relationship between fish parasite communities and water quality, metazoan parasites were examined in 140 specimens of the Mozambique tilapia (Oreochromis mossambicus) sampled in three lakes in the Limpopo Province, namely the Luphephe–Nwanedi Dams (regarded as unpolluted), the Flag Boshielo Dam (regarded as moderately polluted) and a return water dam on a mine site (regarded as polluted). The monogenean parasites Cichlidogyrus halli, digenean larval stages of Clinostomum and Diplostomum spp. and a gryporynchid cestode were found in or on O. mossambicus in all the sampled sites. The distribution of monogeneans (Cichlidogyrus sclerosus, Cichlidogyrus dossoui, Cichlidogyrus tilapiae, Scutogyrus longicornis and three Enterogyrus spp.), metacercarial stages of two digeneans (Neascus and Acanthostomum spp.) and nematodes (an unidentified nematode, Contracaecum sp., Paracamallanus cyathopharynx and Procamallanus laevionchus) was limited to the unpolluted and moderately polluted lakes. Larval stages of Diplostomum sp. were present in O. mossambicus collected from the unpolluted and polluted sites. The variability of the calculated infection indices (prevalence, mean abundance and mean intensity) and the parameters of species richness and diversity suggest that the structure of parasite communities are affected by the pollution levels of the water. The unpolluted reference site had the highest species richness and the highest overall parasite abundance values.

Impact of microcystin-producing cyanobacteria on reproductive success of Lymnaea stagnalis (Gastropoda, Pulmonata) and predicted consequences at the population level

Our previous studies showed that microcystin (MC)-accumulation in the gastropod Lymnaea stagnalis and effects on life-history traits (survival, growth, and fecundity) varied according to age, exposure pathway (MC-producing cyanobacteria or dissolved MC), and presence or not of additional non-toxic food. This study investigated effects of exposure to MC-producing cyanobacteria or to dissolved MC of parent and of parent and egg masses of L. stagnalis on hatching success, duration of embryonic development and neonate survival. Secondly, the potential impact of MC-producing cyanobacterial proliferations (blooms) on L. stagnalis population growth, depending on bloom frequencies and recovery duration of life traits after exposure, was evaluated using a modelling approach. Experimental results showed that embryonic development was shortened in case of parent exposure to toxic cyanobacteria. Parent and eggs exposure to dissolved MC extended embryonic development and reduced hatching percentage, suggesting a permeability of egg masses to MC. Whatever exposure, neonate survival was reduced. Neonates exposed to cyanobacteria accumulated MCs 24 h after hatching, suggesting very early cyanobacteria ingestion. Modelling results showed that L. stagnalis population growth was influenced by the recovery time of life-history traits after exposure. When setting the latest at 6 weeks according to previous experiments, a frequency of one to four blooms per year strongly affected population dynamics and induced up to a 80-weeks delay compared to control in time required for populations to grow from 1 to 1000 individuals. Results are discussed in terms of impact of intoxication pathways on parents, eggs and neonates, and on population dynamics of L. stagnalis.

Towards the development of an embryotoxicity bioassay with terrestrial snails: screening approach for cadmium and pesticides

Currently no bioassays are available to assess the embryotoxicity of chemicals with terrestrial soil invertebrates. We therefore presented a new method for embryotoxicity testing with snail eggs: a relevant biological material that incubates in soil and that can be exposed to contaminants from leachates and soil solution. The effects of aqueous solutions of two herbicide formulations, Reglone(®) (active ingredient (a.i.), diquat) and Roundup(®) or its a.i., glyphosate, of a surfactant (Agral(®) 90, a.i., nonylphenol polyethoxylates) and of cadmium (Cd) were studied. Endpoints were the hatching success and observations of embryo abnormalities after exposure. Roundup(®) was found to be more toxic than its a.i. alone (EC50(a.i.)=18 mg/l and about 1300 mg/l, respectively). Reglone(®) (EC50(a.i.)=0.72 mg/l) and Agral(®) (EC50(a.i.) ≈ 50 mg/l) were also tested together, revealing that Reglone(®) accounted for more than 99% of the mixture's toxicity. An antagonistic interaction between the two substances was found. For Cd (EC50=3.9 mg/l), a significant transfer from exposure medium to eggs was emphasized, particularly affecting the albumen. Abnormalities of embryogenesis in non-hatched embryos depended on the substance and the concentration considered.

Age-related differential sensitivity to cadmium in Hyalella curvispina (Amphipoda) and implications in ecotoxicity studies

The standardization of toxicity tests requires the selection of the most suitable test species and their developmental stages, as well as the selection of the appropriate assay matrix and the evaluation of the sensitivity of the test species to the reference toxicants. International protocols recommend the use of the amphipod Hyalella azteca from the Northern Hemisphere for sediment toxicity tests. We selected the widely distributed amphipod Hyalella curvispina, representative of pleustonic, epiphitic and zoobenthic assemblages in austral South America, as test species to be used in regional studies. Our goals were to evaluate the sensitivity of three developmental stages of H. curvispina to cadmium as a reference toxicant and to select the most suitable age and exposure time for aquatic ecotoxicity assessment. The three ages were highly susceptible to cadmium, with sensitivities: neonates > adults > juveniles. Our results validate the use of the native H. curvispina as a standard species for ecotoxicological assessment studies.