Micro x-ray absorption spectroscopic analysis of arsenic localization and biotransformation in Chironomus riparius Meigen (Diptera: Chironomidae) and Culex tarsalis Coquillett (Culicidae)

Toxicokinetics of silver and silver sulfide nanoparticles in Chironomus riparius under different exposure routes

Engineered nanoparticles released into surface water may accumulate in sediments, potentially threatening benthic organisms. This study determined the toxicokinetics in Chironomus riparius of Ag from pristine silver nanoparticles (Ag NPs), a simulating aged Ag NP form (Ag₂S NPs), and AgNO₃ as an ionic control. Chironomid larvae were exposed to these Ag forms through water, sediment, or food. The potential transfer of Ag from larvae to adult midges was also evaluated. Results revealed higher Ag uptake by C. riparius upon exposure to Ag₂S NPs, while larvae exposed to pristine Ag NPs and AgNO₃ generally presented similar uptake kinetics. Uptake patterns of the different Ag forms were generally similar in the tests with water or sediment exposures, suggesting that uptake from water was the most important route of Ag uptake in both experiments. For the sediment bioaccumulation test, uptake was likely a combination of water uptake and sediment particles ingestion. Ag uptake via food exposure was only significant for Ag₂S NPs. Ag transfer to the terrestrial compartment was low. In our environmentally relevant exposure scenario, chironomid larvae accumulated relatively high Ag concentrations and elimination was extremely low in some cases. These results suggest that bioaccumulation of Ag in its nanoparticulate and/or ionic form may occur in the environment, raising concerns regarding chronic exposure and trophic transfer. This is the first study determining the toxicokinetics of NPs in Chironomus, providing important information for understanding chironomid exposure to NPs and their potential interactions in the environment.

Development of a novel microfluidic device to study metal geochemistry in situ using X-ray fluorescence microprobe spectroscopy

The study of in situ microscale biogeochemical processes represents a major challenge in the environmental sciences. The combination of microfluidic devices with X-ray fluorescence microprobe spectroscopy may address this need, but typical materials used in these devices attenuate the X-rays needed to analyze key elements of interest, such as Fe or As. In this work, a method is presented for fabricating an etched silicon microfluidic device that is sealed with a 30 µm thin glass window that is sufficiently transparent for X-ray fluorescence microprobe spectroscopy. The capabilities of these devices for X-ray microprobe spectroscopy are demonstrated using an Fe (hydr)oxide solid that is loaded with As and then infused with sulfide, on beamline 4-BM at NSLS-II, resulting in time-variant Fe precipitation reactions and As sorption. Key results include in situ X-ray fluorescence time-series maps of Fe, As and a Br flow tracer, as well as spot XANES at both the Fe K edge and As K edge. Additionally, multiple energy mapping is used to examine the spatial speciation of As over time. The results of this work clearly demonstrate the capabilities of this novel microfluidic system that can be analyzed using X-ray fluorescence microprobe spectroscopy and can be made to study a wide range of complex microscale geochemical systems.

Growth and Safety Assessment of Feed Streams for Black Soldier Fly Larvae: A Case Study with Aquaculture Sludge

The production of food is an intensive source of environmental impact. In aquaculture, one source of impact is solid waste, which contains high concentrations of minerals, other nutrients, and metals. The larvae of Hermetia illucens are capable of consuming this material, but applying technology that is based on these larvae for managing waste streams, like those from aquaculture, requires careful examination of safety risks. A study is performed examining the growth performance of larvae that were fed on solid aquaculture waste. Subsequently, a thorough analysis of safety risks from inorganics, with detailed the results on microelements that have previously received little attention in the literature, is performed to serve as a guideline for how to assess the safety of waste streams such as these. Findings confirm existing results in the literature that Cd is bioaccumulative, but also that other elements, including Hg, Mn, and especially K, are bioaccumulative. To the authors' knowledge, this is the first research where the accumulation of Ag is also tested. The results of these tests are explained within the context of regulations in various countries where Hermetia illucens is cultivated, serving as a reference for practitioners to rigorously screen out high risk feed streams that they may consider using as feed sources. It is intended that these references and the demonstrated accumulation of a range of elements motivate comprehensive industry safety practices when evaluating new feed sources.

Encaged Chironomus riparius larvae in assessment of trace metal bioavailability and transfer in a landfill leachate collection pond

Household wastes may constitute a vector of environmental contamination when buried, in particular through degradation and production of leachates containing significant trace metal (TM) concentrations that may constitute a serious risk to biota. The objectives of this study were to assess the bioavailability and transfer potential of various TMs present in water and sediments in a reservoir receiving landfill leachates. An active biomonitoring approach was adopted consisting of exposing naive laboratory organisms in cages deployed in the field. Aquatic insects such as Chironomus riparius larvae are good candidates since they represent key organisms in the trophic functioning of aquatic ecosystems. The results show that water, suspended particles, and sediments were significantly contaminated by various TMs (As, Cd, Cu, Ni, Pb, and Zn). Their contribution to the transfer of TMs depends, however, on the specific element considered, e.g., Cd in sediments or Pb in both suspended particles and sediments. The internal fate of TMs was investigated according to their fractionation between an insoluble and a cytosolic fraction. This approach revealed different detoxification strategies capable of preventing the induction of deleterious effects at the individual scale. However, the accumulation of several TMs in C. riparius larvae tissues may also represent a significant load potentially transferable to higher trophic levels.

Trophic fate of inorganic and methyl-mercury in a macrophyte-chironomid food chain

Dietary transfer of mercury (Hg) is central for its effects on higher trophic animals, nonetheless, its driving parameters and characteristics are not well understood. Here we measured Hg species transfer (uptake) from the macrophyte Elodea nuttallii -mimicking tissues incorporation in sediments after decay- to Chironomus riparius. Methyl-Hg (MMHg) was more transferable than inorganic Hg (IHg) from plant's intracellular and cell wall compartments. After 10-d-long exposure, MMHg was predominantly found in MMHg form in the cytosolic compartment (S) of chironomids, while IHg showed similar concentrations in S and insoluble debris (P) compartments. After cessation of Hg species exposure (depuration), only MMHg resulted in a bioaccumulation factor >1. Toxicokinetics modelling indicated a demethylation of MMHg in the S fraction and its concomitant storage in the P fraction as IHg during both uptake and depuration, revealing an elimination and detoxification mechanism. Our data support that MMHg is more transferable than IHg to sensitive subcellular targets as well as bioavailable fraction in chironomids, in line with field studies showing higher MMHg transfer than IHg in food webs. Hence our data point out macrophytes as a potential Hg source to benthic food webs to be considered for enhancing aquatic environment protection during phytoremediation programs.

Bioaccumulation Dynamics of Arsenate at the Base of Aquatic Food Webs

Periphyton is an important food source at the base of freshwater ecosystems that tends to bioconcentrate trace elements making them trophically available. The potential for arsenic-a trace element of particular concern due to its widespread occurrence, toxicity, and carcinogenicity-to bioconcentrate in periphyton and thus be available to benthic grazers is less well characterized. To better understand arsenate bioaccumulation dynamics in lotic food webs, we used a radiotracer approach to characterize accumulation in periphyton and subsequent trophic transfer to benthic grazers. Periphyton bioconcentrated As between 3,200-9,700-fold (dry weight) over 8 days without reaching steady state, suggesting that periphyton is a major sink for arsenate. However, As-enriched periphyton as a food source for the mayfly Neocloeon triangulifer resulted in negligible As accumulation in a full lifecycle exposure. Additional studies estimate dietary assimilation efficiency in several primary consumers ranging from 22% in the mayfly N. triangulifer to 75% in the mayfly Isonychia sp. X-ray fluorescence mapping revealed that As was predominantly associated with iron oxides in periphyton. We speculate that As adsorption to Fe in periphyton may play a role in reducing dietary bioavailability. Together, these results suggest that trophic movement of As in lotic food webs is relatively low, though species differences in bioaccumulation patterns are important.

Remote Sensing and Reflectance Profiling in Entomology

Remote sensing describes the characterization of the status of objects and/or the classification of their identity based on a combination of spectral features extracted from reflectance or transmission profiles of radiometric energy. Remote sensing can be benchtop based, and therefore acquired at a high spatial resolution, or airborne at lower spatial resolution to cover large areas. Despite important challenges, airborne remote sensing technologies will undoubtedly be of major importance in optimized management of agricultural systems in the twenty-first century. Benchtop remote sensing applications are becoming important in insect systematics and in phenomics studies of insect behavior and physiology. This review highlights how remote sensing influences entomological research by enabling scientists to nondestructively monitor how individual insects respond to treatments and ambient conditions. Furthermore, novel remote sensing technologies are creating intriguing interdisciplinary bridges between entomology and disciplines such as informatics and electrical engineering.

Increase in developmental instability in a field-collected Chironomus population maintained under laboratory conditions

In order to be a relevant indicator of exposure towards teratogenic stressors, morphological defects should not be passed on to the next generation. In this study, we compare morphological variations in Chironomids collected from a contaminated river stretch with those of their progeny, reared in uncontaminated sediment under laboratory conditions. We focused on mentum defects (deformities, fluctuating asymmetry and mean shape change), measured by geometric morphometrics. We observed no significant variation in deformity rate between the parental generation and its progeny. On the contrary, we observed a significant increase in fluctuating asymmetry and a significant decrease in mentum centroid size in the offspring. Our results suggest that shape defects are not caused by direct exposure to teratogenic stressors alone. We propose four hypotheses to explain this: (a) teratogenic contaminants are present in egg-clutches, (b) contaminants at the sampling site have mutagenic effects, (c) costs of tolerance, and (d) contamination-induced genetic impoverishment.

Trophic Transfer of Arsenic from an Aquatic Insect to Terrestrial Insect Predators

The movement of energy and nutrients from aquatic to terrestrial ecosystems can be substantial, and emergent aquatic insects can serve as biovectors not only for nutrients, but also for contaminants present in the aquatic environment. The terrestrial predators Tenodera aridifolia sinensis (Mantodea: Mantidae) and Tidarren haemorrhoidale (Araneae: Theridiidae) and the aquatic predator Buenoa scimitra (Hemiptera: Notonectidae) were chosen to evaluate the efficacy of arsenic transfer between aquatic and terrestrial environments. Culex tarsalis larvae were reared in either control water or water containing 1000 µg l(-1) arsenic. Adults that emerged from the control and arsenic treatments were fed to the terrestrial predators, and fourth instar larvae were fed to the aquatic predator reared in control or arsenic contaminated water. Tenodera a. sinensis fed arsenic-treated Cx. tarsalis accumulated 658±130 ng g(-1) of arsenic. There was no significant difference between control and arsenic-fed T. haemorrhoidale (range 142-290 ng g(-1)). Buenoa scimitra accumulated 5120±406 ng g(-1) of arsenic when exposed to arsenic-fed Cx. tarsalis and reared in water containing 1000 µg l(-1) arsenic. There was no significant difference between controls or arsenic-fed B. scimitra that were not exposed to water-borne arsenic, indicating that for this species environmental exposure was more important in accumulation than strictly dietary arsenic. These results indicate that transfer to terrestrial predators may play an important role in arsenic cycling, which would be particularly true during periods of mass emergence of potential insect biovectors. Trophic transfer within the aquatic environment may still occur with secondary predation, or in predators with different feeding strategies.