Effects of different routes of exposure to metals on bioaccumulation and population growth of the cyclopoid copepod Paracyclopina nana

Arsenic bioaccumulation and biotransformation in the marine copepod Tigriopus japonicus under chronic dietborne and waterborne exposure

Arsenic (As) can be transferred along the food chain, while little is known about the toxic effects of dietborne As on marine copepods. In this study, we investigated the short-term and long-term effects of waterborne and dietborne As exposure on the bioaccumulation and biotransformation, as well as developmental toxicity of Tigriopus japonicus. Under acute As exposure, As bioaccumulation increased and reached a plateau with increasing exposure concentration. Moreover, As accumulation at dietborne exposure was 4.3 and 5.7 times greater than that at control group for AsIII and AsV, respectively. At chronic As exposure, As accumulation increased continuously with exposure time, with a 2.8-day extension of development time and a 45% reduction in 10-d fecundity under dietborne exposure compared to control, whereas 2.3-day extension of development time and a 20% reduction in 10-d fecundity were observed under waterborne exposure. Among As species, inorganic As had the highest concentrations, but the proportion of inorganic As decreased from 89% to 63% during 4 to 21 d of exposure, suggesting the conversion of inorganic As to organic As. The organic As was dominated by arsenobetaine (AsB, 13-25%), followed by monomethylarsenic (MMA, 8-25%). These results suggest that dietborne exposure has more pronounced toxic effects on T. japonicus, but the toxicity of As could be reduced through biotransformation under chronic exposure. Therefore, the arsenic species should be considered when assessing As toxicity.

Synergistic and additive effects of microplastic, nickel and pyrene on survival, reproduction, and egestion of a tropical copepod

Coastal tropical ecosystems provide livelihood for millions of people but are at the same time exposed to an increasing intensity of diverse anthropogenic stressors, including pollution. Nevertheless, the combined effects of pollutants on marine ecosystems are poorly understood, particularly regarding lower trophic levels (plankton) and tropical ocean. We exposed the tropical copepod Centropages velificatus to 4-5 concentrations of a heavy metal (nickel), an oil compound (pyrene) and microplastic (PET), either alone or in combination, and measured their egestion, reproduction, and mortality rates. Microplastic alone did not have any effect on pellet or egg production of copepods, whereas nickel reduced egg production rate at concentrations ≥1 µg L-1 and pyrene reduced both egg and pellet production rates at concentrations ≥1 nM. The addition of nickel and pyrene to PET - microplastic resulted in a reduction similar to one caused by nickel or pyrene alone, suggesting an additive effect. In contrast, a combination of nickel and pyrene had a synergistic effect, with a strong reduction in survival, egg and pellet production. Our results suggest that combinations of contaminants that are commonly found in tropical coastal waters have detrimental effects on copepods-the crucial link in the pelagic food web-at lower concentrations than suggested by single stressor studies. This can have an influence on the food web productivity - the basis of fisheries that local communities rely on.

Trace metals exposure in three different coastal compartments show specific morphological and reproductive traits across generations in a sentinel copepod

The effect of exposure from several compartments of the environment at the level of individuals was rarely investigated. This study reports the effect of contaminants from varied compartments like sediment resuspension, elutriation from resuspended sediment (extract) and seawater spiked trace metal mixtures (TM) on morphological and reproductive traits of the pelagic bioindicator copepod Eurytemora affinis. At the population level of E. affinis, lowest survival was observed in dissolved exposures (TM and extract) in the first generation (G1), showing some adaptation in the second generation (G2). An opposite trend for resuspended sediment showed higher sensitivity in survival at G2. At the individual level, prosome length and volume proved to be sensitive parameters for resuspended sediments, whereas clutch size and egg diameter were more sensitive to TM and extract. Although the generation of decontamination (G3, no exposure), showed a significant recovery at the population level (survival % along with clutch size) of E. affinis exposed to resuspended sediment, morphological characteristics like prosome length and volume showed no such recovery (lower than control, p < 0.05). To the contrary, dissolved exposure showed no significant recovery from G1 to G3 on neither survival %, clutch size, egg diameter, prosome volume, but an increase of prosome length (p < 0.05). Such tradeoffs in combatting the stress from varied sources of toxicity were observed in all exposures, from G1 to G3. The number of lipid droplets inside the body cavity of E. affinis showed a significant positive correlation with trace metal bioaccumulation (p < 0.01) along with a negative correlation (p < 0.05) with survival and clutch size in each treatment. This confirms the inability of copepods to utilize lipids under stressful conditions. Our study tenders certain morphological and reproductive markers that show specificity to different compartments of exposure, promising an advantage in risk assessment and fish feed studies.

Responses of the copepod Eurytemora affinis to trace metal exposure: A candidate for sentinel to marine sediment resuspension effects

Our study reports the ability of Eurytemora affinis to indicate certain responses in 96 h when exposed to resuspended sediment from a polluted site (PS, Seine estuary, France), less polluted site (LPS, Canche estuary, France) and dissolved trace metals. Mortality from dissolved trace metal was highest (57.5 %) followed by PS (38.59 %) > LPS (24.04 %). The exposure to PS sediment resulted in significantly lower no. of early larval stage (nauplii < 2), sex-ratio (39.24 % of males) and higher ovigerous female (>10). Eurytemora affinis bioaccumulated high concentrations of copper (27.3 mg/kg), nickel (12.8 mg/kg), lead (21.8 mg/kg) and arsenic (13.7 mg/kg) from PS exposure with significantly lower bioaccumulation of metals from LPS. The bioconcentration factor (BCF) was highest from dissolved toxicity (>2000) followed by PS that showed significantly higher BCF for Nickel and Copper, compared to LPS. The responses of E. affinis to different matrices exemplify its role as a sentinel.

Investigating the Ecotoxicity of Select Emerging Organic Contaminants Toward the Marine Copepod Gladioferens pectinatus

Estuarine ecosystems are recipients of anthropogenic stressors released from land-based activities. The aim of the present study was to investigate the ecotoxicological hazards of organic contaminants toward the estuarine copepod Gladioferens pectinatus using acute and chronic testing. Most chemicals demonstrated acute toxicity and influenced development of the copepods. Further research should be conducted to investigate these chemicals and their mixtures using long-term, multigenerational testing to characterize mechanisms of toxicity. Environ Toxicol Chem 2022;41:792-799. © 2022 SETAC.

Single toxicity of arsenic and combined trace metal exposure to a microalga of ecological and commercial interest: Diacronema lutheri

Eco-toxicological assays with species of economic interest such as Diacronema lutheri are essential for industries that produce aquaculture feed, natural food additives and also in drug developing industries. Our study involved the exposure of a single and combined toxicity of arsenic (As V) to D. lutheri for the entire algal growth phase and highlighted that a combined exposure of As V with other essential (Copper, Cu; Nickel, Ni) and non-essential (Cadmium, Cd; Lead, Pb) trace metals reduced significantly the cell number, chlorophyll a content, and also significantly increased the de-epoxidation ratio (DR) as a stress response when compared to the single toxicity of As V. Arsenic, as one of the ubiquitous trace metal and an active industrial effluent is reported to have an increased bio-concentration factor when in mixture with other trace metals in this study. In the combined exposure, the concentration of total As bio-accumulated by D. lutheri was higher than in the single exposure. Hence, polluted areas with the prevalence of multiple contaminants along with the highly toxic trace metals like As can impose a greater risk to the exposed organisms that may get further bio-magnified in the food chain. Our study highlights the consequences and the response of D. lutheri in terms of contamination from single and multiple trace metals in order to obtain a safer biomass production for the growing need of natural derivatives.

First transcriptome of the copepod Gladioferens pectinatus subjected to chronic contaminant exposures

Contaminants are often at low concentrations in ecosystems and their effects on exposed organisms can occur over long periods of time and across multiple generations. Alterations to subcellular mechanistic pathways in response to exposure to contaminants can provide insights into mechanisms of toxicity that methods measuring higher levels of biological may miss. Analysis of the whole transcriptome can identify novel mechanisms of action leading to impacts in exposed biota. The aim of this study was to characterise how exposures to copper, benzophenone and diclofenac across multiple generations altered molecular expression pathways in the marine copepod Gladioferens pectinatus. Results of the study demonstrated differential gene expression was observed in cultures exposure to diclofenac (569), copper (449) and benzophenone (59). Pathways linked to stress, growth, cellular and metabolic processes were altered by exposure to all three contaminants with genes associated with oxidative stress and xenobiotic regulation also impacted. Protein kinase functioning, cytochrome P450, transcription, skeletal muscle contraction/relaxation, mitochondrial phosphate translocator, protein synthesis and mitochondrial methylation were all differentially expressed with all three chemicals. The results of the study also suggested that using dimethyl sulfoxide as a dispersant influenced the transcriptome and future research may want to investigate it's use in molecular studies. Data generated in this study provides a first look at transcriptomic response of G. pectinatus exposed to contaminants across multiple generations, future research is needed to validate the identified biomarkers and link these results to apical responses such as population growth to demonstrate the predictive capacity of molecular tools.

Multigenerational study of life history traits, bioaccumulation, and molecular responses of Pseudodiaptomus annandalei to cadmium

Metal pollution provide a substantial challenge for environmental health. This study investigated the multigeneration effects of cadmium on populations of the copepod species Pseudodiaptomus annandalei, exposed to a sublethal concentration, 40 µg/L of cadmium (Cd), over 10 generations. At the end of each generation, copepod individuals were collected to estimate fecundity, bioaccumulation, and real time qPCR quantification of selected differentially expressed genes to evaluate Cd effects and sex-specific responses of copepods across multiple generations. Our results revealed a sex-specific accumulation of Cd integrating 10 successive generations. The concentration of Cd was significantly higher (p < 0.05) in males than in females. We also observed a generational increase in Cd accumulation. Fecundity increased, with the exception of the first generation, possibly as a compensation for a decrease of copepod population size under Cd exposure. Protein expression of copepods exposed to Cd occurred in a sex-specific manner. Hemerythrin was mostly up-regulated in both copepod sexes exposed to Cd with males having the highest expression levels, while heat shock protein 70 was mostly up-regulated in males and down-regulated in female copepods, both exposed to Cd. Although copepods are known to develop adaptive mechanisms to tolerate toxic chemicals, continuous exposure to metals could lead to the bioaccumulation of metals in their offspring through maternal transfer and direct uptake from the medium over several generations. As a consequence, increased metal concentrations in copepods could result in physiological damage, reducing their fitness, and possibly compromise copepod population structures. This study showed that mortality, life history traits and molecular responses of a copepod species provided important toxicological endpoints and bio-markers for environmental risk assessments. Environmental pressure resulting from continuous exposure to persistent pollutants like Cd, could have evolutionary significance. The tendency for copepods to selectively adapt to a toxic environment through modifications, could increase their chance of survival over a long term.

A New Approach to Quantifying Bioaccumulation of Elements in Biological Processes

Simple Summary

The bioaccumulation of elements (e.g., heavy metals) in living organisms (e.g., animals) is vitally important from at least two points of view: the growth and development of the organisms themselves and remediation of the polluted environment. So far, bioaccumulation has been characterized by the bioaccumulation factor (BAF), which is the ratio between the concentration of elements in the organism to the concentration in the matrix (water, soil, etc.). This factor is a good measure of bioaccumulation in ecosystems in which an organism lives from the beginning of their lives to the moment of investigation. However, especially in laboratory experiments, when organisms at a given stage of development are introduced to the system and contain some non-zero concentration of an element, the BAF can lead to misinterpretation. Therefore, we propose a new measure called the bioaccumulation index (BAI), which is the relative increase in the concentration of a given element in the organism to its initial concentration after the experiment. We proved, on the basis of data published by other authors, that the BAI was much more valid for the interpretation of bioaccumulation in these cases.

Abstract

Bioaccumulation, expressed as the bioaccumulation factor (BAF), is a phenomenon widely investigated in the natural environment and at laboratory scale. However, the BAF is more suitable for ecological studies, while in small-scale experiments it has limitations, which are discussed in this article. We propose a new indicator, the bioaccumulation index (BAI). The BAI takes into account the initial load of test elements, which are added to the experimental system together with the biomass of the organism. This offers the opportunity to explore the phenomena related to the bioaccumulation and, contrary to the BAF, can also reveal the dilution of element concentration in the organism. The BAF can overestimate bioaccumulation, and in an extremal situation, when the dilution of element concentration during organism growth occurs, the BAF may produce completely opposite results to the BAI. In one of the examples presented in this work (Tschirner and Simon, 2015), the concentration of phosphorous in fly larvae was lower after the experiment than in the younger larvae before the experiment. Because the phosphorous concentration in the feed was low, the BAF indicated a high bioaccumulation of this element (BAF = 14.85). In contrast, the BAI showed element dilution, which is a more realistic situation (BAI = −0.32). By taking more data into account, the BAI seems to be more valid in determining bioaccumulation, especially in the context of entomoremediation research.

Intergenerational effects of resuspended sediment and trace metal mixtures on life cycle traits of a pelagic copepod

Multiple stressors like metal toxicity, organic compounds and sediment pollution from the Seine estuary are raising concern and novel toxicological approaches are needed to better assess and monitor the risk. In the present study, the copepod Eurytemora affinis from the Seine, was exposed to two different sources of contaminants, which were resuspended polluted sediments and a mixture of trace metals (dissolved phase). The exposure continued for four generations (F0, F1, F2, F3) where F0 is a generation for acclimation to the exposure condition and F3 is a generation for decontamination followed without any exposure, to detect possible maternal carryover effects of pollutants (F0 - F2) and the role of recovery (in F3). Higher accumulation of metals resulted in higher mortalities at both exposure conditions, with particularly F1 being the most sensitive generation showing highest bioaccumulation of metals, highest mortality, and smallest population size. Copper accumulation was highest of all metals in mixture from both the resuspended sediment and the combined trace metal treatment. A significantly lower naupliar production was seen in copepods exposed to resuspended sediment compared to trace metal exposed copepods. However, the decontamination phase (F3) indicated that E. affinis pre-exposed to resuspended sediment had a higher ability to recover the total population size, increase naupliar production, and depurate accumulated Cu. The population exposed to a trace metal mixture showed lower recovery and lower ability to discharge accumulated toxic metals indicating its greater effect on our experimental model when compared to resuspended sediment.