Environmental-Friendly Contamination Assessment of Habitats Based on the Trace Element Content of Dragonfly Exuviae

Abstract

We tested the usefulness of exuviae as an environmentally friendly method for exploring the variability of the trace element contents of protected insect populations without killing specimens. It is a notable characteristic of dragonflies that they are good ecological indicators for both aquatic and terrestrial habitat quality. Thus, we investigated the trace element accumulation in different stages of dragonflies: larva, exuvia, and adult. Using microwave plasma atomic emission spectrometry (MP-AES), we analysed the concentrations of Al, Ba, Cr, Cu, Fe, Mn, Pb, Sr and Zn. We found that the trace element contents of exuviae are a good proxy of the trace element contents of both the larvae and the adults. We conclude that exuvia is useful for assessing the environmental health of aquatic ecosystems. It is an environmentally friendly method and it can be used even in the case of protected dragonfly species. 2 of 10 their larvae stage in aquatic habitats and use a wide range of terrestrial habitats as adults, and they are important predators in aquatic and terrestrial ecosystems [19][20][21][22].Aquatic insects can accumulate elements such as Al, Cd, Cr, Cu, Fe, Mg, Mn and Zn from sediment and from food [23]. In aquatic insects, the concentrations of Hg, Cd, Ni, Cr, As, Pb, Cu, Ti, Zn and Mn change with size, life cycle stages and different bioaccumulation patterns [24]. There are only a few reports dealing with the changes in trace element concentration during different developmental stages [25]. Among these stages, dragonfly adults increase their bioaccumulation potential because they feed on other invertebrates [21]. Larvae and exuviae are also useful to detect accumulation and element bioavailability [24].Accumulated trace metals can be detoxified and excreted in aquatic invertebrates [26]. Trace elements become associated with the calcium in the exoskeleton matrix. They may be absorbed on the surface of the exoskeleton or bind to the inner exoskeleton matrix after uptake [27,28]. During metamorphosis, the protein and lipid content alter; stored resources and decomposing cellular structures are metabolized. Metamorphosis influences metal concentration by metal excretion; thus, the concentration of these metals decreases in the body. Mechanisms of contaminant loss include the exoskeleton as exuvia; the importance of this pathway also depends on the contaminant [21,29,30]. The decontamination process under conditions of an intensive intake of trace elements to an organism is the production of excrement [27].Earlier studies demonstrated that the river clubtail (Gomphus flavipes (Stylurus flavipes)) (Odonata: Gomphidae; Linnaeus, 1758) is a sensitive indicator of pollution [31,32]. This species is a characteristic of large lowland rivers in Europe [33,34] and in Hungary [35]; thus, this species was chosen for our study. The aim of our study was to investigate the trace element accumulation in different stages of the dragonfly to test whether the exuviae may be used as a tool for contamination level assessment. We an...

Mercury Bioavailability in Fluvial Sediments Estimated Using Chironomus riparius and Diffusive Gradients in Thin-Films (DGT)

“…However, it is in line with results by Cid et al [42], which showed similar concentrations between nymphs and adults of the mayfly Ephoron virgo collected in mercury contaminated river sites. Similarly, specimens of the dragonfly Gomphus flavipes collected in a metal contaminated river showed similar body burdens between larvae and adults for Cu and Zn and in some sites also for Cr, Pb, and Sr [12]. These examples show that metamorphosis does not necessarily imply a significant elimination of metals, especially when the main accumulation organ is not the exoskeleton, as proved for Hg and Cd in E. virgo moults [42] and for Hg in C. riparius [13].…”

“…These organisms, among which is the well-known test organism Chironomus riparius, are prey for other invertebrates and for fish, so they are involved in mercury biomagnification along the trophic chains. Moreover, these insects develop into terrestrial adults, which may transport mercury from the aquatic to the terrestrial environment, potentially exerting harmful effect on insectivorous predators such as birds and bats [9][10][11][12].…”

Puparial Cases as Toxicological Indicators: Bioaccumulation of Cadmium and Thallium in the Forensically Important Blowfly Lucilia sericata

“…Previous studies have reported that one mechanism of detoxification among insects involves the exuviae, the coverings shed by the final larval stage or newly emerged adults. In the dragonfly species Gomphus flavipes , Simon et al ( 2019 ) found that, for certain metals—Al, Fe, and Mn—and under certain living conditions, exuviae contained higher metal concentrations than either larvae or adults, demonstrating that molting plays a role in detoxification. Similarly, Kraus et al ( 2014 ) reported that some trace elements, such as Zn, Cd, and Cu, were lost during metamorphosis, leading to 2- to 125-fold higher concentrations in larvae compared to adults, and a higher exposure risk for predators of larvae compared to predators of adults.…”

“…However, it should be considered that metals can be also excreted in the meconium of last-instar larvae or newly emerged adults. Indeed, Simon et al ( 2019 ) reported that <10% of the metal burden lost during metamorphosis could be attributed to the exuviae whereas more than 50% was typically lost through meconium. This latter mechanism is more likely to play a role for Cd, as the concentration of Cd in adults was lower than in larvae, while concentrations in larvae and puparial cases were not statistically different.…”

Holo- and hemimetabolism of aquatic insects: Implications for a differential cross-ecosystem flux of metals

“…A possible explanation for the lack of bioamplification of these metals seen within our study may have been low metal assimilation efficiencies and/or high rates of elimination within our collected organisms, most likely due to the softness of individual metals (Williams, 1982;Croteau et al, 2007;Kraus et al, 2014). For example, the reduction in metal concentrations through metamorphosis may have occurred through the shedding of the exoskeleton during molts (Timmermans and Walker, 1989;Bardeggia and Alikhan, 1991;Dallinger and Rainbow, 1993;Kraus et al, 2014;Simon et al, 2019). Simon et al (2019) found significantly higher levels of the class A and borderline metals Al, Fe and Mn in dragonfly exuviae than in larvae and adults.…”