Distribution of Experimentally Added Selenium in a Boreal Lake Ecosystem.

Human activities have increased the release of selenium (Se) to aquatic environments, but information about the trophic transfer dynamics of Se in Canadian boreal lake systems is limited. In the present study, Se was added as selenite to limnocorrals (2-m-diameter, 3000-L in situ enclosures) in a boreal lake in northwestern Ontario to reach nominal concentrations of 1 and 10 µg Se/L in triplicate each for 77 d, and 3 additional limnocorrals were controls with no Se added. Total Se concentrations were determined in water, sediment, periphyton, benthic macroinvertebrates, zooplankton, and reproductively mature female fathead minnows (Pimephales promelas; added on day 33) collected throughout (and at the end of) the exposure period. Mean measured water Se concentrations in the control, 1-, and 10-µg/L treatments were 0.12, 1.0, and 8.9 µg/L. At the end of exposure (day 77), enrichment functions ranged from 7772 L/kg dry mass in the 8.9-µg/L treatment to 23 495 L/kg dry mass in the 0.12-µg/L treatment, and trophic transfer factors for benthic macroinvertebrates ranged from 0.49 for Gammaridae to 2.3 for Chironomidae. Selenium accumulated in fathead minnow ovaries to concentrations near or above the current US Environmental Protection Agency criterion (15.1 µg/g dry mass for fish ovary/egg) in the 1.0- and 8.9-µg/L treatments, suggesting that, depending on aqueous Se speciation, such exposures have the potential to cause Se accumulation in fish to levels of concern in cold-water, boreal lake systems. Environ Toxicol Chem 2019;38:1954-1966. © 2019 SETAC.

Chironomid larvae enhance phosphorus burial in lake sediments: Insights from long-term and short-term experiments.

Tube-dwelling macrozoobenthos can affect lake ecosystems in myriad ways, including changes in nutrient fluxes across the sediment-water interface. The pumping activity of chironomid larvae reinforces the transport of solutes between sediment and water. The transport of oxygen into the area surrounding the burrows generates oxidized compounds such as iron(oxy)hydroxides, which results in an additional phosphorus (P) sorption capacity similar to that of oxidized sediment surfaces. In the present study, the effect of the oxidized burrow walls of Chironomus plumosus on P binding capacity and P binding forms was tested in the laboratory using sediments with differing iron contents and varying numbers of chironomid larvae. In an additional long-term experiment, lake sediment naturally rich in iron was incubated under oxic conditions for 165 days, followed by a 3.5-year anoxic period. These experiments showed that: (1) Under oxic conditions the cumulative P uptake by sediments was dependent on larval densities. (2) The P that accumulated both at the sediment-water interface and in the oxidized burrow walls was mainly present as reductive soluble P (iron-bound P). Surprisingly, the amount of P released during the anoxic period in the long-term experiment was independent of the amount of P previously taken up during the oxic period since a portion of P was permanently retained in the sediment. The increase in alkaline soluble metal-bound P (NaOH-SRP) in formerly colonized sediments is a strong indication that the excessive P fixation by reductive soluble iron triggers the subsequent formation of stable iron phosphate minerals such as vivianite. Our study shows that P fixation that is induced by chironomid larvae is not always a completely reversible phenomenon, even after the emergence of the larvae and the re-establishment of anoxic conditions in the sediment.

Ameliorative efficacy of bioencapsulated Chironomous larvae with Shilajit on Zebrafish (Danio rerio) exposed to Ionizing radiation.

Using Zebrafish (Danio rerio) as a model organism, we evaluated the radioprotective and antioxidant effects of the Indian traditional medicine Shilajit exposed to X-Ray. The Zebrafish were divided into three experimental groups and control group, each group containing ten fish. The three experimental fish groups, group I, group II and group III were fed with 3, 5 and 7ppm shilajit encapsulated Chironomous larvae and group IV served as a control fed with non- encapsulated larvae. After 60 days of feeding trial, fish were irradiated with X-Ray at a single acute dose of 1Gy. 72h of post-irradiation, each experimental fish were observed for its morphological, behavioral, clinical symptoms, antioxidant levels and DNA damage were evaluated. Among the experimental groups 5ppm shilajit encapsulated Chironomous larvae fed fish group shows the most significant radioprotective effects compared with control and other experimental fish groups. The present study indicates that shilajit have significant radioprotective and antioxidant enhancing capability. The humus substance of shilajit may be the factor responsible to react with radiation-derived or radiation related reactive species on zebrafish.

Individual-based model of Chironomus riparius population dynamics over several generations to explore adaptation following exposure to uranium-spiked sediments.

Natural populations are chronically exposed to various pollutants over many generations. It is thus crucial to understand and quantify adaptive dynamics of stressed populations in order to increase the relevance of ecotoxicological risk assessment. However, long-term consequences to population exposure are not much studied yet. The present study investigated evolutionary responses of Chironomus riparius populations exposed to uranium (heavy metal pollutant) and to assess the underlying mechanisms. To fulfil our objective, we produced data with organisms exposed to four relevant concentrations of uranium through eight successive generations. We built an individual-based (IBM) model of C. riparius population dynamics to analyse these data and to test several assumptions about the mechanisms involved in the phenotypic changes. The IBM was based on a dynamic energy budget (DEB) model for C. riparius by Pery et al. (2002). DEB models account mathematically for the acquisition and use of energy to describe and predict growth, maintenance, development and reproduction of living organisms. The IBM accounted for the influence of the test conditions on the observations over eight generations and highlighted some trait evolution such as time to emergence and adult size in control conditions. The model was then used to analyse the exposed population data. Our results showed that exposure to uranium led to a phenotypic selection via a differential survival characterised by longer time to emergence and smaller larval maximal size. As a general conclusion, IBMs based on DEB-based modelling developed to analyse multi-generation experiments are very promising for understanding and quantifying long term selection and tolerance mechanisms in a population under toxic stress.

Uranium uptake and depuration in the aquatic invertebrate Chironomus tentans.

Evaluation of aqueous uranium (U) uptake and depuration in larvae of the midge Chironomus tentans were investigated in two separated experiments. First, a static-renewal experiment was performed with 10-d old C. tentans larvae exposed to 300 microg U/L. The animals steadily accumulated U (K(u) = 20.3) approaching steady-state conditions (BAF = 56) in approximately 9-11 d. However, accumulated U was readily depurated (K(d) = 0.36) with U tissue concentration decreasing rapidly within 3 d of the larvae being placed in clean water (t(1/2) = 1.9 d). Also, the growth of C. tentans larvae appeared to decrease after 6-11 d of U exposure, probably due to the reallocation of resources into U detoxification mechanisms. However, growth significantly increased once C. tentans were transferred to clean water. A separate short-term experiment was performed to evaluate the possible mechanism of U uptake in this invertebrate. Results suggested a passive mechanism of U uptake coupled with an active mechanism of U depuration but no details related to the type of mechanisms or pathway was investigated.

Accumulation and chronic toxicity of uranium over different life stages of the aquatic invertebrate Chironomus tentans.

Limited data are available on the effects of uranium (U) exposures on benthic macroinvertebrates, something that would be needed before national or provincial water quality guidelines could be developed. The goal of this study was to evaluate chronic U toxicity and accumulation in the aquatic invertebrate Chironomus tentans. Test organisms were exposed to three aqueous U concentrations (40, 200, and 1,000 microg/L) and an untreated control. Larval growth, adult emergence, and U tissue concentrations at different life stages were evaluated. The measured no-observed-effect concentration (NOEC) and lowest-observed-effect concentration (LOEC) for growth of C. tentans larvae after 10 days of U exposure were 39 and 157 microg/L, respectively. At U concentrations >157 ug/L, there was reduced larval growth of 30% to 40%, which corresponded to reduced adult emergence of 40% to 60%. Despite significant delays in time to adult emergence, there were no significant effects on reproductive output of successfully emerged adults. The F(1) generation C. tentans larvae that were never directly exposed to U, but originated from adult males and females exposed to U during their immature life stages, displayed a significant decrease in 10-day growth that was similar to that observed for the F(0)-exposed larvae. This suggests that the environment of the parental generation can significantly influence the development of the next generation through environmentally induced parental effects. Uranium accumulated in C. tentans immature stages was partially excreted during molting and metamorphosis to the adult stage. However, the elimination of U was not complete and some was still measured in adult midges. Consequently, a minor transfer of U from the aquatic to the terrestrial environment could be expected to occur.

Exposure of Chironomus riparius larvae to uranium: effects on survival, development time, growth, and mouthpart deformities.

Among non-biologically essential metals, data concerning uranium effects on freshwater benthic macroinvertebrates are scarce. The effects of uranium on survival, development time, growth and mouthpart deformities of midge Chironomus riparius were investigated. A 10-day static laboratory bioassay was performed exposing first instar larvae to artificial sediment spiked with four concentrations of uranium (2.97; 6.07; 11.44; 23.84 microg U g(-1) dry wt). As uranium was released from the sediment to the overlying water during this bioassay, both the sediment and the water column act as contamination pathways in giving rise to the observed effects. Significant negative effects on survival, development time, and growth were detected at 6.07, 6.07 and 2.97 microg U g(-1) dry wt, respectively. An LC20 of 2.49 microg U g(-1) dry wt (95% CI=1.48-4.27), and an LC50 of 5.30 microg U g(-1) dry wt (95% CI=3.94-7.25) were estimated. With respect to effects of uranium on larvae mouthpart deformities, we found that the lower the concentrations, the higher the deformity rates. These results highlight the potential impact of uranium at population level in environmentally realistic concentrations.

Predators accelerate nutrient cycling in a bromeliad ecosystem.

Conventional ecological theory predicts that predators affect nutrient cycling by decreasing the abundance or activity of prey. By using a predator-detritivore-detritus food chain in bromeliads, we show that predators can increase nutrient cycling by a previously undescribed, but broadly applicable, mechanism: reducing nutrient export by prey emigration. Contrary to expectations, predation on detritivores increases detrital nitrogen uptake by bromeliads. Predation reduces detritivore emergence and hence export of nitrogen from the system. Detritivores therefore benefit their host plant, but only when predators are present. More generally, our results show that predator loss or extinction can dramatically and unexpectedly affect ecosystem functioning.

Effects of long-chain hydrocarbon-polluted sediment on freshwater macroinvertebrates.

High-molecular weight (> C16) hydrocarbons (HMWHs) are common pollutants in sediments of freshwater systems, particularly urban water bodies. No sediment quality guidelines exist for total hydrocarbons; more emphasis is placed on polyaromatic hydrocarbons, the most toxic component of hydrocarbons. A field-based microcosm experiment was conducted to determine whether unpolluted sediments spiked with synthetic motor oil impair freshwater macroinvertebrate assemblages. Total petroleum hydrocarbon (TPH) concentrations of 860 mg/kg dry weight significantly increased the abundance of Polypedilum vespertinus and Cricotopus albitarsis and decreased the abundance of Paratanytarsus grimmii adults (all Chironomidae), whereas TPH concentrations ranging from 1,858 to 14,266 mg/kg produced a significant reduction in the total numbers of taxa and abundance, with significant declines in the abundance of nine chironomid taxa. About 28% of water bodies surveyed in urban Melbourne, Australia, had TPH concentrations in sediments likely to cause ecological impairment, and about 14% of the water bodies surveyed are likely to have reduced species richness and abundance. Therefore, HMWHs can be a significant pollutant in urban water bodies. Freshwater sediment quality guidelines should be developed for this ubiquitous urban pollutant.

In vitro lethal efficacy of leaf extract of Cannabis sativa Linn on the larvae of Chironomous samoensis Edward: an insect of public health concern.

Leaf extract of C. sativa causes paralysis leading to death in larvae of C. samoensis. The extract brought a drastic change in the morphology of sensilla trichoidea and the general body cuticle. The larvae exposed to the leaf extract also showed a significant reduction in the concentration of Mg and Fe, while Mn showed only slight average increase. Since the sensilla trichoidea has nerve connection, it is expected that the toxic principle of the leaf extract has affected the central nervous system. The significant reduction of the level of Fe indicates that the extract could cause the reduction in oxygen binding capacity of the haemolymph, thereby acting as a respiratory poison in addition to its known role as a neurotoxic substance.

Multilevel effects of sublethal fenitrothion exposure in Chironomus riparius Mg. (Diptera, Chironomidae) larvae.

The effects of fenitrothion exposure on fourth-instar Chimnomus riparius larvae were investigated on biochemical, physiological, and population-level parameters. Biochemical effects were investigated through measurements of acetylcholinesterase and cytosolic superoxide dismutase activities. Water content and dry weight of the larvae were used as physiological parameters, and the emergence rate of adults was used as a descriptor of population-level effects. Results showed that the response of most parameters exhibited a concentration-dependent relationship. Although biochemical parameters proved to be very sensitive, no direct relation was observed with effects at a higher level of biological organization. Perturbations of osmoregulation, as reflected by changes in water content of the larvae, were more directly related with emergence failure. This study demonstrates that the use of several biological parameters can provide complementary information about the effects of chemical exposure. Therefore, use of a multilevel approach in C. riparius seems to be a promising way to diagnose environmental quality.