Oysters and mussels as equivalent sentinels of microplastics and natural particles in coastal environments

Filter-feeder organisms such as oyster and mussels are exposed to particles like microplastics (MPs). Although widely used to monitor MPs contamination, little is known about their performance as sentinels, which are biological monitors accumulating contaminants without significant adverse effects. This study comparatively evaluated the quantitative and qualitative accumulation of MPs by oysters (Crassostrea brasiliana) and mussels (Perna perna) along a gradient of contamination in a highly urbanized estuarine system of Brazil. In the most contaminated site, both species presented the worst status of nutrition and health, and also one of the highest MPs levels reported for molluscs to date (up to 44.1 particles·g^-1). Despite some inter-specific differences, oysters and mussels were suitable and showed an equivalent performance as sentinels, reflecting the gradient condition demonstrated for other contaminants in the region. The similarity in MPs accumulation was also observed for qualitative aspects (polymer composition, sizes, shapes and colors). Particles were mostly <1000 μm, fibrous, colorless and composed by cellulose and polymethyl methacrylate (PMMA). Thus, despite small variations, the usage of C. brasiliana and P. perna is recommended and provides reliable information for environmental levels of microplastics.

Environmental interaction of antimony and arsenic near busy traffic nodes

Antimony (Sb) and arsenic (As) are elements with similar chemistry, toxicity and binding properties, but different environmental risks and prevailing anthropogenic sources. A significant source of Sb contamination is associated with braking in extremely loaded traffic areas, where the produced abrasion dust contains up to 5% wt. of Sb₂S₃. In these same exposure areas, As still originates mostly from the combustion of fossil fuels. Heavily loaded crossroads from three different regions of the Czech Republic (Central Europe) were monitored for Sb content in road dusts, topsoils and reference soils during a two-year season (2016-2017). The same samples were also tested for As content to evaluate current contamination trends of both elements in exposed urban areas. The concentration of Sb varied from 5 to 70 µg g^-1 in topsoils, and from 20 to 350 µg g^-1 in road dusts with the preference for binding to the fine particle fraction (<0.1 mm). The average Sb concentration was up to 60 times the background value and decreased in the order: brake abrasion (10³ µg g^-1) > road dust (10² µg g^-1)> topsoils (10¹ µg g^-1) >> reference soils (<1 µg g^-1). The concentration of As in road dust, topsoils and reference soils had about the same level, 10¹ µg g^-1 indicating a more regional character of As pollution. Correlation factors for Sb/As versus iron (Fe)/organic matter (OM) indicated a more robust correlations in soils compared to road dusts and generally better correlations of Sb compared to As. While arsenic contamination has recently decreased thanks to a massive decline of arsenic emissions, antimony contamination indicates a dangerous trend due to growing automotive traffic.

Statistical determination of crucial taxa indicative of pollution gradients in sediments of Lake Taihu, China

In order to accurately monitor the changes in a freshwater ecosystem in response to anthropogenic stressors, microbe-environment correlations and microbe-microbe interactions were combined to determine crucial indicator taxa in contaminated sediments. The diversity, composition, and co-occurrence pattern of bacterial communities in 23 sediment samples collected from Lake Taihu were explored using 16S rRNA amplicon sequencing analysis. Fisher's exact test showed that the cluster analyses of samples could show a direct correlation between the relative abundance of bacterial communities and the physicochemical properties of the sediment (P < 0.0001), suggesting that bacterial communities can be used to monitor contamination gradients in freshwater sediments. According to the microbe-environment correlation, 24 orders and 60 families were initially identified via indicator species analysis as indicator taxa of different pollution levels. The co-occurrence network further showed that topological features of bacterial communities were clearly different at different pollution levels, although the diversity and composition of bacterial communities displayed similarities between minimally and moderately polluted sites. Indicator taxa were then screened for keystone species, which co-occurrence relationships showed the high degree and low betweenness centrality values (i.e. degree >5, betweenness centrality <1000) of the network. Nine orders and 13 families were finally extracted as crucial indicator taxa of the different pollution levels in eutrophic Lake Taihu. Obtaining crucial indicator taxa from environmental sequences allows to trace increasing levels of pollution in aquatic ecosystems and provides a novel mean to monitor watersheds sensitive to anthropic influences.

Spatial avoidance as a response to contamination by aquatic organisms in nonforced, multicompartmented exposure systems: A complementary approach to the behavioral response

The idea that the hazard of contaminants is exclusively related to their toxic effects does not consider the fact that some organisms can avoid contamination, preventing toxicity. Although inferences about avoidance are made in most behavioral ecotoxicology studies, assessment of the real spatial displacement (organisms moving toward another habitat to escape contamination) is difficult due to the type of exposure (confined and mandatory) used in the bioassays: a forced exposure approach. A complementary approach using nonforced exposure systems to assess how contaminants affect the spatial distribution of organisms in a bicompartmented (toxic or nontoxic) environment has long been described. Recently, this nonforced approach has been developed to include a multi compartmented system in which different samples can be simultaneously tested. The aim of the present review was to describe the importance of the nonforced, multicompartmented exposure approach to simulate a gradient or patches of contamination, to describe the 2 main exposure systems, and to highlight the ecological relevance of including spatial avoidance and habitat preference in ecotoxicological studies. The multicompartmentalization of the system makes it possible to simulate more complex scenarios and therefore include new ecological concepts in bioassays. We also contrasted spatial avoidance in the nonforced exposure systems with the behavioral endpoints measured under other exposure systems. Finally, we showed that the nonforced, multicompartmented exposure approach makes it possible 1) to improve environmental risk assessments by adding the dispersion pattern of organisms in a multihabitat scenario, and 2) to integrate ecological concepts such as recolonization of recovering habitats, loss of habitat connectivity, habitat fragmentation, and contamination-driven metapopulation, which have received limited attention in ecotoxicological studies. Environ Toxicol Chem 2019;38:312-320. © 2018 SETAC.

Avoidance response by shrimps to a copper gradient: Does high population density prevent avoidance of contamination?

Bioassays using the nonforced exposure approach have been shown to be a relevant tool that might complement the traditional ecotoxicological risk assessment. Because the nonforced exposure approach is based on spatial displacement of organisms and the consequent habitat selection processes, the population density might play an important role in the decision to avoid or prefer an ecosystem. Therefore, the aim of the present study was to assess if the avoidance response to contamination, measured in a nonforced exposure system, is density-dependent and how determinant contamination could be for the habitat-selection process in comparison with the population density. The freshwater shrimp Atyaephyra desmarestii was exposed to a copper gradient in a nonforced exposure system formed by 7 interconnected compartments (total volume 600 mL), which contained different copper concentrations. The density treatments used were 3, 5, and 10 organisms per compartment, corresponding to 0.5, 0.8, and 1.7 organisms per 100 mL, respectively. Clearly, the avoidance response to copper was more intense in the population with the lower density: the highest population density showed the lowest avoidance. The concentrations that triggered an avoidance of 50% of the population were 47, 134, and 163 μg L^-1 . In summary, it was observed that shrimps were able to detect and avoid potentially toxic copper concentrations but that the avoidance response was affected by population density. Environ Toxicol Chem 2018;37:3095-3101. © 2018 SETAC.

Habitat fragmentation caused by contaminants: Atrazine as a chemical barrier isolating fish populations

Information on how atrazine can affect the spatial distribution of organisms is non-existent. As this effect has been observed for some other contaminants, we hypothesized that atrazine-containing leachates/discharges could trigger spatial avoidance by the fish Poecilia reticulata and form a chemical barrier isolating upstream and downstream populations. Firstly, guppies were exposed to an atrazine gradient in a non-forced exposure system, in which organisms moved freely among the concentrations, to assess their ability to avoid atrazine. Secondly, a chemical barrier formed by atrazine, separating two clean habitats (extremities of the non-forced system), was simulated to assess whether the presence of the contaminant could prevent guppies from migrating to the other side of the system. Fish were able to avoid atrazine contamination at environmentally relevant concentrations (0.02 μg L^-1), below those described to cause sub-lethal effects. The AC₅₀ (atrazine concentration causing avoidance to 50% of the population) was 0.065 μg L^-1. The chemical barrier formed by atrazine at 150 μg L^-1 (concentration that should produce an avoidance around 82%) caused a reduction in the migratory potential of the fish by 47%; while the chemical barrier at 1058 μg L^-1 (concentration that produces torpidity) caused a reduction in the migratory potential of the fish by 91%. Contamination by atrazine, besides driving the spatial distribution of fish populations, has potential to act as a chemical barrier by isolating fish populations. This study includes a novel approach to be integrated in environmental risk assessment schemes to assess high-tier contamination effects such as habitat fragmentation and population displacement and isolation.

Potential effects of triclosan on spatial displacement and local population decline of the fish Poecilia reticulata using a non-forced system

Triclosan (TCS) is an emerging contaminant of concern in environmental studies due to its potential adverse effects on fish behavior. Since avoidance has been shown to be a relevant behavioral endpoint, our aims were: (i) to determine if TCS is able to trigger an avoidance response in Poecilia reticulata; (ii) to predict the population immediate decline (PID) caused by TCS exposure, by integrating lethality and avoidance responses; and (iii) to verify the overestimation of risk when mortality is assessed under forced exposure. Fish were exposed to TCS in a forced exposure system, to assess mortality, and to a TCS gradient in a non-forced exposure (NFE) system. Two NFE scenarios were simulated: (#1) a spatially permanent gradient, including low and high concentrations; and (#2) a scenario with high concentrations, simulating a local discharge. The fish avoided TCS concentrations as low as 0.2 μg L^-1 (avoidance of 22%). The AC50 obtained from scenario #1 (8.04 μg L^-1) was about 15 times more sensitive than that from scenario #2 (118.4 μg L^-1). In general, up to the highest concentration tested (2000 μg L^-1), the PID was determined by the avoidance. Mortality from the forced exposure was overestimated (48 h-LC50 of 1650 mg L^-1), relative to the NFE. The reduced mortality in a non-forced environment does not imply a lower effect, because part of the population is expected to disappear by moving towards favorable environments. TCS is a potential environmental disturber, since at environmentally relevant concentrations (<2 μg L^-1) it could cause a decline in the fish population.

Predicting the effects of copper on local population decline of 2 marine organisms, cobia fish and whiteleg shrimp, based on avoidance response

The present study focuses on avoidance response to predict population decline of the marine fish Rachycentron canadum (cobia) and larvae of the estuarine shrimp Litopenaeus vannamei (whiteleg shrimp). Avoidance of approximately 60% was recorded for the cobia fry exposed to 1.0 mg Cu/L, 1.60 mg Cu/L, and 1.80 mg Cu/L. For the shrimp larvae, avoidance was approximately 80% for all Cu concentrations. The population decline of cobia fry was conditioned by avoidance in lower concentrations. However, in higher concentrations mortality begins to play an important role. The displacement toward uncontaminated habitats might determine shrimp population decline. A Cu-contaminated environment can determine the habitat selection of both species and, therefore, their local population decline.

The interaction of heavy metals and nutrients present in soil and native plants with arbuscular mycorrhizae on the riverside in the Matanza-Riachuelo River Basin (Argentina)

This study assessed the contamination by heavy metals (Cr, Cu, Pb, Zn), and nutrients (N, P) in soils and native plants, and the effect of the concentration of those elements with the density of arbuscular-mycorrhizal (AM) spores in soil and colonization in roots from the riverside of the Matanza-Riachuelo River Basin (MRRB). The concentration of metals and nutrients in soils and plants (Eleocharis montana, Cyperus eragrostis, Hydrocotyle bonariensis) increased from the upper sites (8 km from headwaters) to the lower sites (6 km from the mouth of the Riachuelo River) of the basin. AM-colonization on the roots of H. bonariensis and spore density in soil decreased as the concentrations of metals in soil and plant tissues increased from the upper to lower sites of the basin within a consistent gradient of contamination associated with land use, soil disturbance, population, and chemicals discharged into the streams and rivers along the MRRB. The general trends for all metals in plant tissue were to have highest concentrations in roots, then in rhizomes and lowest in aerial biomass. The translocation (TF) and bioconcentration (BCF) factors decreased in plants which grow from the upper sites to the lower sites of the basin. The plants tolerated a wide range in type and quantity of contamination along the basin by concentrating more metals and nutrients in roots than in aboveground tissue. The AM spore density in soil and colonization in roots of H. bonariensis decreased with the increase of the degree of contamination (Dc) in soil.

Changes in zooplankton communities along a mercury contamination gradient in a coastal lagoon (Ria de Aveiro, Portugal)

The main objective of this paper was to evaluate the impact of mercury on the zooplankton communities' structure and functioning and their bioaccumulation patterns along a contamination gradient in a temperate coastal lagoon. Our results demonstrated that total abundance was not negatively affected by Hg contamination, since the most contaminated areas presented the highest values, being the copepod Acartia tonsa the dominant species, which means that it is a very well adapted and tolerant species to mercury. Nevertheless, negative effects were observed in terms of species diversity, since the most contaminated areas presented the lowest values of species richness, evenness and heterogeneity. Moreover, the spatial mercury gradient was reflected on the bioaccumulation patterns of the zooplankton communities. This reinforces the idea that zooplankton can be considered as an important vehicle of mercury transfer through the food pelagic web since it constitutes a primordial food resource for several commercial fish species.