Effects of cypermethrin on marine plankton communities: a simulated field study using mesocosms

Fish predation affects invertebrate community structure of tropical temporary ponds, with downstream effects on phytoplankton that are obscured by pesticide pollution

Aquatic biota of tropical temporary ponds typically experience a wide range of stressors that can drive the structure and dynamics of natural communities. Particularly in regions with intense agricultural activity, aquatic biota may not only experience predation pressure but also stress from pesticides that inadvertently enter the ponds. We increasingly understand how these different sources of stress affect classic model taxa under controlled laboratory conditions, but how predators and pesticides may jointly affect pond invertebrate communities is still unclear, particularly for tropical systems. Here, we conducted an outdoor mesocosm experiment to study how fish predation combined with exposure to an environmentally relevant concentration of the commonly used insecticide cypermethrin (0.8 ng/L) affects the structure of invertebrate communities, and its potential effects on leaf litter decomposition and invertebrate grazing efficiency as measures of ecosystem functioning. A total of seven invertebrate taxa were recorded in the mesocosm communities. Fish predation effectively lowered the number of invertebrate taxa, with fish mesocosms being dominated by high densities of rotifers, associated with lower phytoplankton levels, but only when communities were not simultaneously exposed to cypermethrin. In contrast, cypermethrin exposure did not affect invertebrate community structure, and neither fish predation nor cypermethrin exposure affected our measures of ecosystem functioning. These findings suggest that predation by killifish can strongly affect invertebrate community structure of tropical temporary ponds, and that downstream effects on phytoplankton biomass can be mediated by exposure to cypermethrin. More broadly, we contend that a deeper understanding of (tropical) temporary pond ecology is necessary to effectively manage these increasingly polluted systems.

Protective effects of 5-aminolevulinic acid against toxicity induced by alpha-cypermethrin to the liver-gut-microbiota axis in zebrafish

To explore whether and how 5-aminolevulinic acid (ALA) can relieve the toxicity to the liver-gut-microbiota axis caused by alpha-cypermethrin (α-CP), adult zebrafish were exposed to α-CP (1.0 µg L-1) with or without 5.0 mg L-1 ALA supplementation. In the present work, the calculated LC50 of α-CP+ALA was 1.15 μg L-1, increasing about 1.16-fold compared with that of α-CP group (0.99 μg L-1), which indicated that ALA can alleviate the toxicity of α-CP. ALA also alleviated the histopathological lesions in the liver and gut induced by α-CP. Transcriptome sequencing of the liver showed that ALA rescues the differential expression of genes involved in the oxidation-reduction, heme metabolism, and complement activation pathways associated with dysfunctions induced by α-CP, and these findings were verified by RT-qPCR analysis and detection of the activities of enzymes in the liver-gut axis. The gut microbiota 16S rRNA sequencing results showed that α-CP alone induced gut microbial dysbiosis, which was efficiently antagonized by ALA due to decreasing the relative abundances of Cetobacterium and 3 major pathogens, and increasing the relative abundances of beneficial genera. Taken together, the results indicate that ALA might be a promising candidate for attenuating the adverse effects caused by pesticide-induced environmental pollution.

Sublethal effects on Simocephalus vetulus (Cladocera: Daphnidae) of pulse exposures of cypermethrin

Pyrethroids are among the most widely applied insecticides worldwide and cypermethrin is the pyrethroid most used in Argentina. Pesticides used in crops can reach adjacent watercourses through runoff and may lead to non-target fauna receiving toxic pulse exposures. The aim of this study was to determine the effects of cypermethrin pulse exposures on the widely distributed crustacean Simocephalus vetulus. The 48h-LC50 of cypermethrin for S. vetulus was determined at 0.18 ± 0.09 μg/L. To assess the effects of cypermethrin under environmentally realistic exposures, two experiments were performed. In the first one, specimens were exposed for 90 min to cypermethrin at 0.02 (T1), 0.2 (T2) and 1 μg/L (T3), transferred to clean water and monitored for 24 h as regards survival and feeding rates; specimens exposed to T2 and T3 concentrations showed significant lower feeding rates than those in the control group. In the second experiment, specimens were exposed for 90 min every 7 days and monitored over 25 days; S. vetulus showed lower cumulative fecundity and reproduction rates at all concentrations tested, and lower population growth at the highest concentration. All exposure concentrations lay within reported environmental concentrations and risk assessment indicated risk (RQ > 1), suggesting that sensitive species would be affected by such pulse exposures of cypermethrin. The present study thus suggests that ongoing agricultural practices affect the non-target invertebrates in streams adjacent to crops.

Horizontal and vertical distribution of sea lice larvae (Lepeophtheirus salmonis) in and around salmon farms in the Bay of Fundy, Canada

The sea louse, Lepeophtheirus salmonis, is parasitic to salmonid species in the Northern Hemisphere and has become a widespread biological and economic problem for the salmon farming industry. A better understanding is needed of their spatial distribution and early life history to disrupt the life cycle of the sea louse. In this study, sea lice larval densities within salmon farms, between salmon farms and reference sites, and at various depths were quantified using both plankton pumps and plankton nets. Farm sites exhibited significantly higher densities than reference sites; however, these densities dropped an order of magnitude at a distance of 100 m from the cages. The majority of the larvae captured in the study were nauplii (93%), and densities ranged from 0 to 10 larvae/m³ . Free-swimming sea lice larvae were found to exhibit a diel cycle where nauplii larvae were in deeper waters (10-17 m) during the day and in surface waters (1-6 m) during the night. The results of this study suggest that the early life-history stages of sea lice originate from and may remain close to active salmon farms, creating a self-sustaining population.

Alkyl polyglucoside compound influences freshwater plankton community structure in floating field mesocosms

Synthetic surfactants in cleaners and detergents commonly contaminate freshwater systems, therefore use of low-toxicity alternatives is becoming increasingly important. Alkyl polyglucosides (APGs) derived from natural products are less toxic than synthetic surfactants, and degrade rapidly reducing chemical exposure time. However, single species toxicity tests showed APGs have toxic effects on aquatic primary producers and zooplankton, and that species demonstrate different sensitivities to APGs. Furthermore, species unaffected by APGs directly may be indirectly affected by removal of a food source or changes in predator densities, thereby changing plankton community structure. To determine the effects of APGs on plankton communities under environmental conditions, floating mesocosms were deployed in a shallow pond in southeast Georgia, USA and dosed with 0, 0.01, 2.5, 5, or 10 mg L^-1 APG. Zooplankton community composition and abundance, phytoplankton abundance (as chlorophyll a), and water column dissolved oxygen concentration were determined weekly for 1 month. Zooplankton abundance decreased primarily due to loss of copepods, and community composition shifted toward small-bodied cladocerans (Bosmina sp.), and chlorophyll a concentrations declined by up to 81 % following exposure to APG concentrations of 2.5 mg L^-1 or greater. Concentrations of dissolved oxygen never dropped below 5.70 mg L^-1, but the observed declines of ~2 mg L^-1 could become stressful during periods of high water temperatures. Nevertheless, the APG-induced shift from copepod to cladoceran dominated communities and decrease in autochthonous carbon availability has important implications for food availability and quality to higher trophic levels such as planktivorous fishes.

Polycyclic aromatic hydrocarbons alter the structure of oceanic and oligotrophic microbial food webs

One way organic pollutants reach remote oceanic regions is by atmospheric transport. During the Malaspina-2010 expedition, across the Atlantic, Indian, and Pacific Oceans, we analyzed the polycyclic aromatic hydrocarbon (PAH) effects on oceanic microbial food webs. We performed perturbation experiments adding PAHs to classic dilution experiments. The phytoplankton growth rates were reduced by more than 5 times, being Prochlorococcus spp. the most affected. 62% of the experiments showed a reduction in the grazing rates due to the presence of PAHs. For the remaining experiments, grazing usually increased likely due to cascading effects. We identified changes in the slope of the relation between the growth rate and the dilution fraction induced by the pollutants, moving from no grazing to V-shape, or to negative slope, indicative of grazing increase by cascade effects and alterations of the grazers' activity structure. Our perturbation experiments indicate that PAHs could influence the structure oceanic food-webs structure.

Ethylene vinyl acetate polymer as a tool for passive sampling monitoring of hydrophobic chemicals in the salmon farm industry

Current monitoring programs are focused on hydrophobic chemicals detection in aquatic systems, which require the collection of high volumes of water samples at a given time. The present study documents the preliminary use of the polymer ethylene vinyl acetate (EVA) as a passive sampler for the detection of a hydrophobic chemical used by salmon industries such as cypermethrin. Initially, an experimental calibration in laboratory was performed to determine the cypermethrin equilibrium between sampler and aquatic medium, which was reached after seven days of exposure. A logarithm of partitioning coefficient EVA-water (logKEVA-W) of 5.6 was reported. Field deployment of EVA samplers demonstrated average concentrations of cypermethrin in water to be 2.07 ± 0.7 ng L(-)(1) close to salmon cages, while near-shore was 4.39 ± 0.8 ng L(-)(1). This was a first approach for assessing EVA samplers design as a tool of monitoring in water for areas with salmon farming activity.

Physiological responses of three marine microalgae exposed to cypermethrin

The effects of cypermethrin on physiological responses of three typical marine microalgal species Skeletonema costatum (Bacillariophyceae), Scrippsiella trochoidea (Dinophyceae), and Chattonella marina (Raphidophyceae), were investigated by 96-h growth tests in a batch-culture system. The 96-h median inhibition concentrations (IC(50)) were 71.4, 205, and 191 μg L(-1) for S. costatum, S. trochoidea, and C. marina, respectively. Quick and significant physiological responses occurred when algal cells were exposed to cypermethrin, and all biochemical parameters varied significantly within 6- or 12-h exposure. Cypermethrin affected algal growth, protein content, and superoxide dismutase (SOD) activity by stimulation at low concentrations (1, 5 μg L(-1)) and inhibition at high concentrations (>50 μg L(-1)). A general increase in malondialdehyde (MDA) level was observed in all test groups, which suggested that the toxic effects of cypermethrin were probably exerted through free radical generation. These results suggest that the activation of SOD and promotion of protein at early exposure are important to counteract the oxidative stress induced by cypermethrin, and the inactivation of SOD may be crucial to the growth inhibition of microalgae by cypermethrin.

Aquatic life water quality criteria derived via the UC Davis method: II. Pyrethroid insecticides

Aquatic life water quality criteria were derived for five pyrethroids using a new methodology developed by the University of California, Davis (TenBrook et al.2010). This methodology was developed to provide an updated, flexible, and robust water quality criteria derivation methodology specifically for pesticides. To derive the acute criteria, log-logistic SSDs were fitted to the medium-sized bifenthrin,cyfluthrin, and cypermethrin acute toxicity data sets while the X-cyhalothrin and permethrin acute data sets were larger, and Burr Type III SSDs could be fitted to these data sets. A review of the cyfluthrin acute criterion revealed that it was not protective of the most sensitive species in the data set, H. azteca, so the acute value was adjusted downward to calculate a more protective criterion. Similarly, the cypermethrin criteria were adjusted downward to be protective of H. azteca.Criteria for bifenthrin, X-cyhalothrin, and permethrin were calculated using the median fifth percentile acute values while the cyfluthrin and cypermethrin criteria were calculated with the next lowest acute value (median first percentile). Chronic data sets were limited in all cases, so ACRs were used for chronic criteria calculations, instead of statistical distributions. Sufficient corresponding acute and chronic data were not available for bifenthrin, cypermethrin, or permethrin, so a default ACR was used to calculate these chronic criteria while measured ACRs were used for cyfluthrin and X-cyhalothrin. A numeric scoring system was used to sort the acute and chronic data, based on relevance and reliability, and the individual study scores are included in the Supporting Information.According to the USEPA (1985) method, the data sets gathered for these five pyrethroids would not be sufficient to calculate criteria because they were each missing at least one of the eight taxa required by that method. The USEPA (1985)method generates robust and reliable criteria, and the goal of creating the UCDM was to create a method that also yields statistically robust criteria, but with more flexible calculation methods to accommodate pesticide data sets of varied sizes and diversities. Using the UCDM, acute and chronic water quality criteria were derived for bifenthrin (4 and 0.6 ng/L, respectively), cyfluthrin (0.3 and 0.05 ng/L, respectively), cypermethrin (1 and 0.2 ng/L, respectively), X-cyhalothrin (1 and 0.5 ng/L,respectively), and permethrin (10 and 2 ng/L, respectively). Water quality criteria for these five pyrethroids can be used by environmental managers to control the increasing problem of surface water contamination by pesticides.

Retrospective qualitative analysis of ecological networks under environmental perturbation: a copper-polluted intertidal community as a case study

The coast of Chañaral Bay in northern Chile has been affected by copper mine wastes for decades. This sustained perturbation has disrupted the intertidal community in several ways, but the mechanisms behind the observed shifts in local biodiversity remain poorly understood. Our main goal was to identify the species (lumped into trophic groups) belonging to the Chañaral intertidal community that, being directly affected by copper pollution, contributed primarily to the generation of the observed changes in community structure. These groups of species were called initiators. We applied a qualitative modelling approach based only on the sign and direction of effects among species, and present a formula for predicting changes in equilibrium abundances considering stress on multiple variables simultaneously. We then applied this technique retrospectively to identify the most likely set of initiators. Our analyses allowed identification of a unique set of four initiators in the studied intertidal system (a group of algae, sessile invertebrates, a group of herbivores and starfish), which were hypothesized to be the primary drivers of the observed changes in community structure. In addition, a hypothesis was derived about how the perturbation affected these initiators. The hypothesis is that pollution affected negatively the population growth rate of both algae and sessile invertebrates and suppressed the interaction between herbivores and starfish. Our analytic approach, focused on identifying initiators, constitutes an advance towards understanding the mechanisms underlying human-driven ecosystem disruption and permits identifying species that may serve as a focal point for community management and restoration.

Toxicological effects of cypermethrin to marine phytoplankton in a co-culture system under laboratory conditions

The growth of three marine phytoplankton species Skeletonema costatum, Scrippsiella trochoidea and Chattonella marina and the response of the antioxidant defense system have been investigated on exposure to commercial cypermethrin for 96 h and 32 days in a co-culture system. Growth of the three species was generally comparable over 96 h with an inoculation of 1:3:6.5 (C. marina:S. trochoidea:S. costatum), with stimulation at 5 μg l(-1) and inhibition under higher concentrations (50, 100 μg l(-1)). However, when inoculating at ratios of 1:1:1 during a 32 day test, S. costatum became the most sensitive species and was significantly inhibited in all test groups under the dual stresses of cypermethrin and interspecies competition. The growth of C. marina was significantly inhibited at the concentrations higher than 5 μg l(-1), while the growth of S. trochoidea was significantly promoted at low concentrations. Superoxide dismutase (SOD) activities significantly increased during 6-12 h exposure periods in test treatments at low concentrations, and enhanced in the control as well due to interspecies competition. The lipid peroxidation product malondialdehyde was enhanced at high concentrations, but did not increase in control and low concentration cultures with high SOD activities, indicating that algal cells activated the antioxidant enzymes promptly to protect the cells from lipid membrane damage. Results from this study suggested that cypermethrin pollution in maricultural sea waters might lead to a shift in phytoplankton community structure from diatom to harmful dinoflagellate species, and thus potentially stimulatory for harmful algal blooms.

The growth behavior of three marine phytoplankton species in the presence of commercial cypermethrin

Toxicity of commercial cypermethrin on the growth of three marine microalgal species, Skeletonema costatum (Bacillariophyceae), Scrippsiella trochoidea (Dinophyceae) and Chattonella marina (Raphidophyceae) was separately investigated by 96 h and 24 d growth tests. The growth was stimulated at low concentrations and inhibited under high concentrations; however, overcompensation was observed at the late period of exposure under high concentrations in 24 d growth tests. The highest stimulation rates were obtained at concentration of 5 microg/L. The 24 h SC10 values were 0.91, 4.17 and 20.4 microg/L for S. costatum, S. trochoidea and C. marina, respectively. The 96 h IC50 values were 75.3, 227 and 114 microg/L for the three species, respectively. Results suggest that cypermethrin level used for sea lice controlling exert a stimulative effect on phytoplankton growth, and might result in the succession of phytoplankton community structure due to different sensitivity of species.

Inferring chemical effects on carbon flows in aquatic food webs: methodology and case study

The majority of ecotoxicological enclosure experiments monitor species abundances at different chemical concentrations. Here, we present a new modelling approach that estimates changes in food web flows from such data and show that population- and food web level effects are revealed that are not apparent from abundance data alone. For the case of cypermethrin in freshwater enclosures, photosynthesis and excretion (d(-1)) of phytoplankton at 3.643 microg L(-1) cypermethrin were 30% lower and 100% higher than in the control, respectively. The ingestion rate of mesozooplankton (d(-1)) was 6 times higher in the treated enclosures than in the control as food concentration increased with insecticide exposure. With increasing cypermethrin concentrations, nanoflagellates progressively relied on phytoplankton as their main food source, which rendered the food web less stable. We conclude that this tool has excellent potential to analyse the wealth of enclosure data as it only needs species abundance and general constraints.

Effects of spinosad and Bacillus thuringiensis israelensis on a natural population of Daphnia pulex in field microcosms

Spinosad, a candidate biological larvicide for mosquito control, was evaluated for its effects on a field population of Daphnia pulex, using Bacillus thuringiensis serovar israelensis (Bti) as a reference larvicide. Microcosms (125L enclosures) were placed in a shallow temporary oligohaline marsh where D. pulex was present. Three concentrations of spinosad (8, 17 and 33 microg L(-1)) and two concentrations of Bti (0.16 and 0.50 microL L(-1)) were applied (5 replicates per concentration, including the controls). Effects of larvicides on D. pulex were evaluated after 2, 4, 7, 14 and 21d of exposure, through measurements of abundance and individual size. Dissipation of spinosad from the water phase was rapid. Four days after treatment, residue concentration represented 11.8%, 3.9% and 12.7% of the initial exposure level for the nominal concentrations of 8, 17 and 33 microg L(-1), respectively. Spinosyns A and D dissipated at similar rates. Analysis of abundance and size structure of the D. pulex population showed an impact of spinosad. Both survival and size structure were affected. However, at the lowest concentration (8 microg L(-1)), population recovered after the first week. In microcosms treated with Bti, the abundance of D. pulex was not affected but the size structure of the population changed after 21d. As compared to laboratory tests, the use of in situ microcosms improved the environmental risk assessment of larvicides, taking into account the influence of environmental factors (e.g., temperature, light, salinity) and intrinsic capacity of recovery of D. pulex under field conditions.

Histological approaches for high-quality imaging of zooplanktonic organisms

The investigation of the internal organization of zooplankton communities provides important information on the plankton biology with special interest for the study of ecological processes. Zooplanktoners can play a structural function as indicators for ecosystem health or stress, but their study using histological techniques is still limited. Here we report that the internal structure of zooplanktonic organisms can be facilely observed by a histological approach that combines optimal fixation and processing with a plastic resin (glycol methacrylate) embedding, resulting in increased tissue resolution. Using copepods, organisms that can dominate zooplankton assemblages, as models, collected from a tropical ecosystem (Paraibuna river, Brazil), we showed fine histological details of their muscular, nervous and digestive systems, structure of appendages and cell features. Critical advantages of this approach are that it permits optimal preservation and adequate handling of the organisms (embedded in agar after fixation) for further histological processing and investigation. This is important because it prevents both mechanically induced artifacts and loss of these diminutive organisms during the different steps of processing. Moreover, embedding in plastic resin showed a superior imaging of copepod internal structures compared to paraffin embedding. The use of glycol methacrylate is advantageous over paraffin/paraplast embedding by avoiding heat damage, tissue retraction and allowing faster embedding procedure and better tissue resolution. The value of histological approaches in enabling high-quality imaging of the internal structure of copepods is particularly important because these organisms can be used as indicators of environmental changes.

Micro-evolution due to pollution: possible consequences for ecosystem responses to toxic stress

Polluting events can change community structure and ecosystem functioning. Selection of genetically inherited tolerance on exposed populations, here referred as micro-evolution due to pollution, has been recognized as one of the causes of these changes. However, there is a gap between studies addressing this process and those assessing effects at higher levels of biological organization. In this review we attempt to address these evolutionary considerations into the ecological risk assessment (ERA) of polluting events and to trigger the discussion about the consequences of this process for the ecosystem response to toxic stress. We provide clear evidence that pollution drives micro-evolutionary processes in several species. When this process occurs, populations inhabiting environments that become polluted may persist. However, due to the existence of ecological costs derived from the loss of genetic variability, negative pleiotropy with fitness traits and/or from physiological alterations, micro-evolution due to pollution may alter different properties of the affected populations. Despite the existence of empirical evidence showing that safety margins currently applied in the ERA process may account for pollution-induced genetic changes in tolerance, information regarding long-term ecological consequences at higher levels of biological organization due to ecological costs is not explicitly considered in these procedures. In relation to this, we present four testable hypotheses considering that micro-evolution due to pollution acts upon the variability of functional response traits of the exposed populations and generates changes on their functional effect traits, therefore, modifying the way species exploit their ecological niches and participate in the overall ecosystem functioning.

Atrazine effects on meiobenthic assemblages of a modular estuarine mesocosm

Atrazine is a widely used herbicide in the US found at levels ranging from <10 ng/L to 62.5 microg/L in estuaries throughout the southeast. Effects of atrazine on estuarine meiobenthic assemblages chronically exposed to environmentally relevant concentrations are unknown. The purpose of our research was to assess effects of atrazine on meiobenthos at concentrations near the proposed USEPA SWQC (26 microg/L) using modular estuarine salt marsh mesocosms as a field surrogate. Indigenous copepod and nematode densities were assessed after 28 days of exposure in transplanted colonization chambers. Cluster analysis showed a group characterized by low copepod densities, mostly atrazine exposed chambers, and a group containing all but one control chamber. The later group included chambers with high densities of the copepods Paronychocamptus wilsoni and Enhydrosoma baruchi. Compared to controls, copepod densities was approximately 70% lower in atrazine chambers, with three of the most common copepod species (E. baruchi, Onychocamptus sp. and P. wilsoni) showing an average of 50-70% reduction in population densities (p<0.05). Although nematode density did not differ between atrazine and control chambers, the nematode-to-copepod ratio was significantly higher in atrazine (9.95+/-7.61; p=0.011) than in control chambers (0.61+/-0.35). Our findings suggest that chronic exposures over multiple generations to atrazine at concentrations near the proposed USEPA SWQC could have significant effects on the abundance and composition of estuarine meiobenthic copepod assemblages.