The use of sediment analogues to study the uptake of pollutants by chironomid larvae

Mechanisms influencing the impact of microplastics on freshwater benthic invertebrates: Uptake dynamics and adverse effects on Chironomus riparius

Chironomids inhabit freshwater benthic ecosystems which are prone to microplastic contamination. This work aimed at understanding the factors and mechanisms influencing microplastic uptake and related adverse effects on Chironomus riparius, by exploring an extensive project database, conducting a literature review, and performing an agent-based model to explore trends in data. Results reveal that high concentrations of small microplastics fill the gut of fourth instar C. riparius (99.7 %). Ingested microplastics had an average size of 38-61 μm, presenting slower elimination rates than undigested organic or mineral particles. Ingestion rates of microplastics depend mainly on encounter rates, and therefore on available concentrations, until reaching a plateau corresponding to the maximum gut volume. Short-term toxicity of microplastics seems to result from damage to gut epithelium, with inflammatory reactions, production of reactive oxygen species, and a negative energy balance exacerbated by the lack of food (organic matter). Long-term toxicity is characterized by a reduction in larval body length and increase in mean time to emergence, seemly from increased energy costs rather than a decrease in nutrient absorption. Wild chironomids already present microplastics in their guts and environmental concentrations in hotspots may already exceed no effect concentrations. Therefore, environmental exposure to microplastics may induce adverse effects to wild C. riparius in freshwater benthic ecosystems, which could compromise their ecologic role as deposit-feeders (e.g., reducing their nutrient cycling ability) and key-stone species in aquatic food webs.

A Reduced Model for Bioconcentration and Biotransformation of Neutral Organic Compounds in Midge

A bioconcentration factor (BCF) database and a toxicokinetic model considering only biota-water partitioning and biotransformation were constructed for neutral organic chemicals in midge. The database contained quality-reviewed BCF and toxicokinetic data with variability constrained to within 0.5 to 1 log unit. Diverse conditions in exposure duration, flow set-up, substrate presence, temperature, and taxonomic classification did not translate into substantial variability in BCF, uptake rate constant (k₁ ), or depuration rate constant (k_T ), and no systematic bias was observed in BCFs derived in unlabeled versus radiolabeled studies. Substance-specific biotransformation rate constants k_M were derived by difference between the calculated biota-water partitioning coefficient (K_BW ) and experimental BCF for developing a midge biotransformation model. Experimental midge BCF was modeled as BCF = K_BW /(1 + k_M/ k₂ ) with log k_M (k_M in h^-1 ) = -0.37 log K_OW - 0.06T (in K) + 18.87 (root mean square error [RMSE] = 0.60), log k₁ (k₁ in L kg_wet.wt^-1  h^-1 ) = -0.0747 W (body weight in mg_wet.wt ) + 2.35 (RMSE = 0.48). The K_BW value was estimated using midge biochemical composition and established polyparameter linear free energy relationships, and the diffusive elimination rate constant (k₂ ) was computed as k₂  = k₁ /K_BW. The BCF model predicted >85% of BCFs that associated with neutral organic compounds (log K_OW  = 1.46 - 7.75) to within 1 log-unit error margin and had comparable accuracy similar to amphipod or fish models. A number of outliers and critical limitations of the k_M model were identified and examined, and they largely reflected the inherent limitation of difference-derived k_M , the lack of chemical diversity, and inadequate temperature variation in existing data. Future modeling efforts can benefit from more BCF and toxicokinetic observations of BCF on structurally diverse chemicals for model training, validation, and diagnosis. Environ Toxicol Chem 2021;40:57-71. © 2020 SETAC.

Investigating arsenic bioavailability and bioaccumulation by the freshwater oligochaete Lumbriculus variegatus

The complex and variable composition of natural sediments makes it difficult to predict the bioavailability and bioaccumulation of sediment-bound contaminants. Several approaches, including an experimental model using artificial particles as analogues for natural sediments, have been proposed to overcome this problem. For this work, we applied this experimental device to investigate the uptake and bioaccumulation of As(III) by the freshwater oligochaete Lumbriculus variegatus. Five different particle systems were selected, and particle-water partition coefficients for As(III) were calculated. The influence of different concentrations of commercial humic acids was also investigated, but this material had no effect on bioaccumulation. In the presence of particulate matter, the bioaccumulation of As(III) by the oligochaetes did not depend solely on the levels of chemical dissolved but also on the amount sorbed onto the particles and the strength of that binding. This study confirms that the use of artificial particles may be a suitable experimental model for understanding the possible interactions that may occur between contaminants and particulate matter. In addition, it was found that the most hydrophobic resin induced an increase in arsenic bioavailability, leading to the highest bioaccumulation to L. variegatus compared with animals that were exposed to water only.

Evaluation of pollutant exposure by chemical and biological markers in a Mediterranean French urban stream: a step for in situ calibration of multixenobiotic resistance transporter expression as biomarker in Chironomidae larvae

This study was aimed at semi-quantifying the membrane density of multixenobiotic resistance (MXR) transporters in Chironomidae Orthocladiinae larvae from an urban stream by ELISA assay. The relationships between the MXR transporter membrane density and limnological parameters and pollutant concentrations, 16 priority polycyclic aromatic hydrocarbons (PAHs), as per the US Environmental Protection Agency (EPA) and seven polychlorobiphenyl congeners (PCBs), were assessed. Midge larvae were collected, and limnological parameters and pollutant concentrations were measured in three sites of a French Mediterranean urban stream, two located after sewage treatment plants, and one closed to the river mouth, and in two additional sites, one on the stream tributary, and one in a non-urbanized stream located in the same region. Results show that the PAH and PCB contamination levels are different between sites and that some congener concentrations are above their threshold toxic effect level (TEL). The MXR transporter membrane density was significantly higher in larvae from the tributary, the most polluted site, as compared with larvae from the non-urbanized stream. The MXR transporter density was positively correlated with 10 of the 16 US-EPA PAH concentrations and the increase in the MXR transporter density seems to be due to the US-EPA PAH concentrations that were above their TEL. No relations with PCB concentrations or limnological parameters were found. The results suggest that the MXR transporter membrane density in Chironomidae larvae could be an interesting biological marker of PAH exposure in freshwater ecosystems.

The impact of particle-bound cadmium on bioavailability and bioaccumulation: A pragmatic approach

Studying the bioavailability of sediment-bound contaminants is complicated by many reasons, such as the variable composition of the particles, their temporal variations, the low levels of contaminant concentrations, their partitioning between diverse aqueous and particulate phases, and the variety of uptake routes that may involved with the biota. Therefore, simple and innovative methodologies should be tested as analogues for natural sediments. Among them, a diverse selection of artificial particles with well-defined surface properties, in the presence and absence of commercially available humic acids, has been proposed and used to investigate the bioavailability of several organic pollutants. For this work, this model was applied to investigate the uptake and accumulation of cadmium by the freshwater oligochaete Lumbriculus variegatus. The results showed that the uptake of the metal depended on the free dissolved Cd(II) species, while the contribution from the particles was negligible. Thus, the extent of cadmium bioaccumulated from each test system could be predicted as a function of the rate of absorption of the free dissolved Cd(II) species. These species were calculated either from the particle-water partition coefficients, or by using the MINEQL+ computer program. In general, the estimated accumulation levels were in good agreement with the experimental results.

Modeling lead bioavailability and bioaccumulation by Lumbriculus variegatus using artificial particles. Potential use in chemical remediation processes

Artificial particles, specifically a diverse selection of chromatographical resins, have been recommended and used as a useful experimental model to predict the bioavailability and bioaccumulation of sediment-bound organic chemicals. In this work the same experimental model was adopted to investigate the bioavailability and bioaccumulation of lead by the freshwater oligochaete Lumbriculus variegatus. Particle-water partition coefficients were also determined. Sand particles and the anionic exchange resin promoted a similar uptake and bioaccumulation of lead. Instead, in the presence of the cationic exchanger the metal was not detected in the animals. For neutral particles, the uptake and accumulation depended on the chemistry of the functional groups at the active sites. In addition, a significant negative correlation was found between bioaccumulation and the particle-water partition coefficients. These studies may help to develop alternative methods for chemical remediation of lead-contaminated aquatic systems.

The influence of salinity on metal uptake and effects in the midge Chironomus maddeni

The influence of different porewater salinities (up to 12 g/L) on the toxicity and bioaccumulation of copper, zinc and lead from metal-spiked sediments was assessed using the midge, Chironomus maddeni. Survival of the larvae was significantly reduced at a porewater salinity of 12 g/L, but no effects were observed at 4 or 8 g/L. Both growth and survival of C. maddeni were reduced after exposure to salt/metal spiked sediments as compared to those exposed to sediments spiked with metals or salt alone. Increased salinity resulted in increased bioaccumulation of copper and zinc, but decreased bioaccumulation of lead. The observed patterns of bioaccumulation were not entirely explained by the modelled free ion activities of the metals, indicating that factors such as osmotic stress, consumption of metal-contaminated sediments or metal interactions may have been important as well. These results highlight the need to consider the influence of existing or potential salinization when undertaking hazard assessments of freshwater systems impacted by contaminants such as trace metals.