Marsupial development in the mysid Neomysis integer (Crustacea: Mysidacea) to evaluate the effects of endocrine-disrupting chemicals

Endocrine disruption in crustaceans: New findings and perspectives

A significant advance has been made, especially during the last two decades, in the knowledge of the effects on crustacean species of pollutants proven to be endocrine disruptors in vertebrates. Such effects have been also interpreted in the light of recent studies on crustacean endocrinology. Year after year, the increased number of reports refer to the effects of endocrine disruptors on several processes hormonally controlled. This review is aimed at summarizing and discussing the effects of several kinds of endocrine disruptors on the hormonal control of reproduction (including gonadal growth, sexual differentiation, and offspring development), molting, and intermediate metabolism of crustaceans. A final discussion about the state of the art, as well as the perspective of this toxicological research line is given.

Larval mosquito management and risk to aquatic ecosystems: A comparative approach including current tactics and gene-drive Anopheles techniques

Genetic engineering of mosquitoes represents a promising tactic for reducing human suffering from malaria. Gene-drive techniques being developed that suppress or modify populations of Anopheles gambiae have the potential to be used with, or even possibly obviate, microbial and synthetic insecticides. However, these techniques are new and therefore there is attendant concern and uncertainty from regulators, policymakers, and the public about their environmental risks. Therefore, there is a need to assist decision-makers and public health stewards by assessing the risks associated with these newer mosquito management tactics so the risks can be compared as a basis for informed decision making. Previously, the effect of gene-drive mosquitoes on water quality in Africa was identified as a concern by stakeholders. Here, we use a comparative risk assessment approach for the effect of gene-drive mosquitoes on water quality in Africa. We compare the use of existing larvicides and the proposed genetic techniques in aquatic environments. Based on our analysis, we conclude that the tactic of gene-drive Anopheles for malaria management is unlikely to result in risks to aquatic environments that exceed current tactics for larval mosquitoes. As such, these new techniques would likely comply with currently recommended safety standards.

Use of Gammarus fossarum (Amphipoda) embryo for toxicity testing: A case study with cadmium

The effects of environmental contaminants on arthropod embryo stages have been poorly investigated in ecotoxicology. Moreover, many of these tests used hatching success as the sole metric, although it is possible to detect many more subtle effects. After a detailed description of embryogenesis in Gammarus fossarum, the present study reports on the sublethal effects of cadmium (Cd) exposure during embryonic development in G. fossarum. Embryos were first directly exposed in multiwell plates throughout the entire embryonic cycle (23 d) to increasing Cd concentrations (0, 1.5, and 3.0 μg/L; 120 embryos/concentration). Then, to assess the representativeness of the gammarid embryo assay performed in multiwell plates, embryos were exposed to similar Cd concentrations through the maternal open brood pouch. Next, to pinpoint sensitive periods of development, embryos were directly exposed to 3.0 μg/L of Cd for shorter periods of time: during gastrulation, organogenesis, and hatching. After hatching, the following parameters were measured in the newborn individuals: 1) body mass; 2) activity of the enzyme phenoloxidase, a key enzyme of the arthropod immune system; and 3) locomotor activity. Phenoloxidase activity was strongly inhibited in newborn individuals of embryos exposed (either in multiwell plates or in the maternal brood pouch) to 3.0 μg/L Cd throughout embryonic development. Furthermore, strong detrimental locomotor effects were observed in newborn individuals of embryos directly exposed to 3.0 μg/L. Exposures for shorter periods of time were not sufficient to induce such effects; no sensitive period could be determined. By bringing new insights into a critical time window of exposure, the gammarid embryo assay could provide a novel and interesting addition to existing bioassays in gammarids. Environ Toxicol Chem 2017;36:2436-2443. © 2017 SETAC.

Environmental safety review of methoprene and bacterially-derived pesticides commonly used for sustained mosquito control

Some pesticides are applied directly to aquatic systems to reduce numbers of mosquito larvae (larvicides) and thereby reduce transmission of pathogens that mosquitoes vector to humans and wildlife. Sustained, environmentally-safe control of larval mosquitoes is particularly needed for highly productive waters (e.g., catchment basins, water treatment facilities, septic systems), but also for other habitats to maintain control and reduce inspection costs. Common biorational pesticides include the insect juvenile hormone mimic methoprene and pesticides derived from the bacteria Bacillus thuringiensis israelensis, Lysinibacillus sphaericus and Saccharopolyspora spinosa (spinosad). Health agencies, the public and environmental groups have especially debated the use of methoprene because some studies have shown toxic effects on non-target organisms. However, many studies have demonstrated its apparent environmental safety. This review critically evaluates studies pertinent to the environmental safety of using methoprene to control mosquito larvae, and provides concise assessments of the bacterial larvicides that provide sustained control of mosquitoes. The review first outlines the ecological and health effects of mosquitoes, and distinguishes between laboratory toxicity and environmental effects. The article then interprets non-target toxicity findings in light of measured environmental concentrations of methoprene (as used in mosquito control) and field studies of its non-target effects. The final section evaluates information on newer formulations of bacterially-derived pesticides for sustained mosquito control. Results show that realized environmental concentrations of methoprene were usually 2-5µg/kg (range 2-45µg/kg) and that its motility is limited. These levels were not toxic to the vast majority of vertebrates and invertebrates tested in laboratories, except for a few species of zooplankton, larval stages of some other crustaceans, and small Diptera. Studies in natural habitats have not documented population reductions except in small Diptera. Bacterial larvicides showed good results for sustained control with similarly limited environmental effects, except for spinosad, which had broader effects on insects in mesocosms and temporary pools. These findings should be useful to a variety of stakeholders in informing decisions on larvicide use to protect public and environmental health in a 'One Health' framework.

Adaptation of the Daphnia sp. acute toxicity test: miniaturization and prolongation for the testing of nanomaterials

Manufacturing of nanomaterials (NMs) is often complex and expensive, and their environmental risks are poorly understood or even unknown. An economization of testing NMs is therefore desirable, which can be achieved by miniaturizing test systems. However, the downsizing of test vessels and volumes can enlarge the surface/volume ratio (SVR) which in turn can affect the bioavailable concentration of adsorbing substances like NMs. The present study focused on the miniaturization of the acute toxicity test with Daphnia magna. The adaptations were verified with three reference substances, the non-adsorbing potassium dichromate (K2Cr2O7) and as potentially highly-adsorbing substances silver nanoparticles (AgNPs) and silver nitrate (AgNO3). The miniaturized test was conducted in 24-well microtiter plates (MT) and simultaneously compared to the OECD standard test (ST). Furthermore, the test duration was prolonged from 48 to 96 h since NMs tend to show effects only after extended exposure. The toxicity of K2Cr2O7 and AgNPs continued to increase within the prolonged test span. The test comparisons with K2Cr2O7 did not reveal any significant differences between ST and MT. AgNO3 toxicity was significantly decreased in MT compared to ST due to the enlarged SVR. The toxicity of AgNPs in MT after 24 h was equal to ST. Contrary to our expectations an exposure longer than 24 h resulted in an increase of AgNP toxicity in MT, possibly due to enhanced dissolution of silver. Microtiter plates are appropriate alternative test vessels for the Daphnia sp. acute toxicity test; thus, its miniaturization is feasible. The enlarged SVR has to be taken into account since it can affect the toxicity of potentially adsorbing substances. Furthermore, the standard test duration of 48 h might underestimate the toxicity of many substances, especially of NMs.

Immunolocalization of estrogen receptor α in Neomysis japonica oocytes and follicle cells during ovarian development

Estrogen induces oocytes development and vitellogenesis in crustacean by interacting with estrogen receptor (ER) subtypes. In the present study, we detect for the first time the ERα in oocytes and follicle cells and hepatopancreas cells of mysis by immunohistochemistry using a specific ERα antibody. ERα was mainly localized in the nuclei of oocytes and follicle cells, while mainly detected in nuclei of oogonia (OG), previtellogenic oocyte (PR) and endogenous vitellogenic oocyte (EN) at previtellogenic and early vitellogenic stage (I-early III). Follicle cells in all stages of ovary (all vitellogenic stages) showed strong ERα positive reaction, and they were able to gradually move to oocytes during the development of oocytes. In addition, ERα was also localized in the nuclei and cytoplasm of four hepatopancreas cells (including E-, R-, F- and B-cell) in all ovary stages. These findings suggest, for the first time to our knowledge, that there could be a close link between oogenesis, follicle cells, hepatopancreas cells and endocrine regulation, and estrogens might be involved in the regulation of oocytes at early ovarian stage in mysis.

Ecdysteroid receptor from the American lobster Homarus americanus: EcR/RXR isoform cloning and ligand-binding properties

In arthropods, ecdysteroids regulate molting by activating a heterodimer formed by the ecdysone receptor (EcR) and retinoid X receptor (RXR). While this mechanism is similar in insects and crustaceans, variation in receptor splicing, dimerization and ligand affinity adds specificity to molting processes. This study reports the EcR and RXR sequences from American lobster, a commercially and ecologically important crustacean. We cloned two EcR splice variants, both of which specifically bind ponasterone A, and two RXR variants, both of which enhance binding of ponasterone A to the EcR. Lobster EcR has high affinity for ponasterone A and muristerone and moderately high affinity for the insecticide tebufenozide. Bisphenol A, diethyl phthalate, and two polychlorinated biphenyls (PCB 29 and PCB 30), environmental chemicals shown to interfere with crustacean molting, showed little or no affinity for lobster EcR. These studies establish the molecular basis for investigation of lobster ecdysteroid signaling and signal disruption by environmental chemicals.

Environmental concentrations of methoprene and its transformation products after the treatment of Altosid® XR Briquets in the city of Richmond, British Columbia, Canada

Water runoff from catch basins treated with Altosid® XR Briquets for mosquito larvae control was sampled at 10 storm drainage pump stations along the outskirts of the city of Richmond, British Columbia, Canada after rainfall events in 2006 to determine the residual concentrations of methoprene and transformation products: citronellic acid, methoprene acid, and 7-methoxycitronellic acid. Runoff of prior-to-treatment, posttreatment, and 150-d-after-treatment was collected. No residues were detected in the prior-to-treatment samples. However, methoprene was detected in posttreatment, and citronellic acid was detected in posttreatment and one 150-d-after-treatment sample. The detected environmental concentrations of methoprene (0.04-0.14 µg/L) and methoprene acid (0.07 µg/L) at pump stations were below known/reported toxicity values to aquatic organisms. However, concentrations detected inside the storm drainage system in catch basins (methoprene 122 µg/L, methoprene acid 1.74 µg/L) and inspection chambers (methoprene 622 µg/L, methoprene acid 20 µg/L, citronellic acid 0.05 µg/L) are known to be toxic to invertebrates, have chronic early-life-stage fish effects, and exceeded the Draft Interim Ontario Water Quality Objective and the numerical benchmarks for protection of amphibians (1.6 µg/L), invertebrates (10 µg/L), and fish (80 µg/L). The limited detection in the present study may have resulted from significant absorption of methoprene to sample bottle walls, substance decay during sample storage before methoprene extraction, flushing of briquettes from catch basins following heavy rainfall, and the burial of briquettes under thick layers of debris.

Limb regeneration and molting processes under chronic methoprene exposure in the mud fiddler crab, Uca pugnax

Insect growth regulator application for wetland mosquito control remains controversial due to the potential for disruption of normal development and growth processes in non-target crustaceans and beneficial arthropods, e.g. Apis mellifera. Concerns include slow-release methoprene formulations and its environmental breakdown products which mimic an endogenous crustacean hormone and retinoids, respectively. Our primary objective was to evaluate the effect that a chronic methoprene exposure would have on male and female Uca pugnax limb regeneration and molting. After single limb autonomy, limb growth and molt stage were monitored every two days while eyestalk ablation was used to induce proecdysis. Dorsal carapace was collected 6 days post-molt to determine protein and chitin content. In post-molt crabs, methoprene-exposed individuals displayed lower percent gain in body weight. Male crabs lost more weight per body volume than females, took significantly longer to proceed through proecdysis than females exposed to 0.1 microg/L methoprene and exhibited significantly elevated frequency for abnormal limb formation at 1.0 microg/L while females displayed no such trend. Methoprene did not significantly alter extractable exoskeleton protein or chitin content. However, variable water-soluble protein expression increased with exposure at 1.0 microg/L (1 ppb) which contributed to overall variability in total protein content. Our findings suggest that adult male U. pugnax possess greater sensitivity to chronic methoprene exposure during limb regeneration and molting, potentially affecting their post-molt fitness. Furthermore, methoprene has the potential to impact post-molt biomass and exocuticle quality.

Mysid crustaceans as standard models for the screening and testing of endocrine-disrupting chemicals

Investigative efforts into the potential endocrine-disrupting effects of chemicals have mainly concentrated on vertebrates, with significantly less attention paid to understanding potential endocrine disruption in the invertebrates. Given that invertebrates account for at least 95% of all known animal species and are critical to ecosystem structure and function, it remains essential to close this gap in knowledge and research. The lack of progress regarding endocrine disruption in invertebrates is largely due to: (1) our ignorance of mode-of-action, physiological control, and hormone structure and function in invertebrates; (2) lack of a standardized invertebrate assay; (3) the irrelevance to most invertebrates of the proposed activity-based biological indicators for endocrine disruptor (ED) exposure (androgen, estrogen, and thyroid); (4) limited field studies. Past and ongoing research efforts using the standard invertebrate toxicity test model, the mysid shrimp, have aimed at addressing some of these issues. The present review serves as an update to a previous publication on the use of mysids for the evaluation of EDs (Verslycke et al. 2004a). It summarizes recent investigative efforts that have significantly advanced our understanding of invertebrate-specific endocrine toxicity, population modeling, field studies, and transgeneration standard test development using the mysid model.