Pesticide Impact on Stream Fauna: With Special Reference to Macroinvertebrates

Assessment of Zambezi River Water Quality Using Macroinvertebrates Population Diversity

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For more realistic assessments of the long-term impacts, field and mesocosm studies are required, as explained in the next section. Some 22 studies on the impacts of neonicotinoids on aquatic communities have been conducted to date.

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Most of them comprise mesocosms that used imidacloprid, with five studies using thiacloprid and one acetamiprid in addition to those two compounds Table S2. These studies were carried out in Japan rice mesocoms , Portugal field trials , Canada, and Germany streams and microcosms. The most striking feature of these studies is their consistency in reporting population and community effects at levels well below the LC50s of the aquatic species tested.

This is unusual, since field or mesocosms studies under realistic scenarios typically report fewer impacts of pesticides and other toxicants than in closed laboratory conditions Cleveland et al. Reduced exposures, due mainly to chemical losses by microbial degradation, hydrolysis and other environmental factors, are usually responsible for the lesser impacts under field conditions Maund et al. Population reductions in the short-term are caused by direct toxicity, but in mesocosms such reductions affect the structure of the macroinvertebrate communities when residues are one or two orders of magnitude lower than the LC50s for most species, as more tolerant taxa tend to increase in numbers to fill the niche vacuum thus created in the ecosystem.

Some of these changes are predictable. In other cases, opportunistic predators e. Interestingly, the negative impacts on predatory copepod populations in rice fields are followed by upsurges of mosquitoes but not of chironomids.

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Consequently, the overall biodiversity of the aquatic communities is negatively affected Pestana et al. Similar impacts are observed in mesocosms treated with thiacloprid at 3.

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This is not surprising, as the HC5 for thiacloprid derived from outdoor stream mesocosms is 0. Figure 6. Relative abundance with respect to controls of aquatic invertebrates in imidacloprid-treated mesocosms. A Communities in rice paddies for different initial concentrations of imidacloprid; dashed lines indicate average reductions. B Invertebrate taxa in rice paddies and streams; vertical dashed line indicates the control. Moreover, many of these populations are decimated and their recovery is either slow or, if there is competition with other species, it does not take place Liess et al.

Nor does the structure of the communities revert to the original situation, because some species disappear while others take over and increase in numbers Beketov et al. These impacts contrast with those caused by other pesticides, which tend to produce a large initial mortality upon target and non-target populations alike but allow the recovery of the species affected within a few weeks van den Brink et al. By contrast, many pyrethroids and organophosphates with the exception of persistent compounds like chlorpyrifos do not produce time-cumulative mortality Parsons and Surgeoner, since their exposure is limited in time Lahr et al.

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Finally, when mayfly nymphs Baetis rhodani and Gammarus fossarum are exposed together to sublethal levels of thiacloprid, the amphipod increases its predation on the nymphs but reduces its shredding of litter at concentrations as low as 0. Imidacloprid also reduces the litter decomposition carried out by stoneflies Pteronarcys dorsata and crane flies Tipula sp.

The implications of these impacts for the larger ecosystem are discussed next. The consequences of all the above for the larger ecosystem have not been studied in detail yet. Difficulties in obtaining long-term experimental data that relates the effects on individual organisms to impacts on ecosystems prevent carrying out such studies. However, it is clear that some predictions can be made from the limited set of observations about the effects on aquatic communities reported so far. At least two main areas of concern can be identified: reduced capacity for decomposition of organic debris by aquatic organisms and starvation of insectivores and other vertebrate fauna that depend on invertebrates as a major or only food source Figure 7.

Effects of lampricide treatment on macroinvertebrate drift in a small, softwater stream

The recycling of organic matter that falls into water bodies is an essential ecosystem function that not only provides food for a wide range of aquatic and benthic organisms but also ensures the water quality is adequate for all other organisms that use it, including ourselves. It is well established that mayfly Ephemeroptera , caddisfly Trichoptera , and stonefly Plecoptera nymphs are the most sensitive aquatic organisms to most pollutants, so they are considered bioindicators of water quality Morse et al.

They are shredders of leaves and other debris found at the bottom of creeks and streams that run through forested and agricultural areas, although not the only ones: larvae of crane flies Tipulidae , black flies Simulidae and other Diptera taxa perform the same function, together with amphipods, ostracods and aquatic isopods. The fact that litter decomposition by stoneflies, crane flies, mayflies and amphipods is significantly reduced by concentrations of neonicotinoids that are currently found in many aquatic environments is of concern Kreutzweiser et al.

Even if some individuals may survive in depleted populations, they still will be unable to carry out the decomposition function properly due to the feeding inhibition caused by these neurotoxicants, which will render those individuals unfit to do their job. To many regulators of chemicals, whether mayflies or other macroinvertebrates are depleted is not important, or at least not as much as the increase in productivity that farmers may obtain from using products like neonicotinoids, although the latter benefits are questionable—see Seagraves and Lundgren, ; Macfadyen et al. Just because macroinvertebrates are not seen, since they are small and live at the bottom of ponds and streams, this does not mean they can be dispensed with.

As Suter and Cormier have argued, these small creatures are present in ecosystems for an important reason Suter and Cormier, Given that more than half of the waters are contaminated Figure 4 with neonicotinoid levels that impair this important ecosystem function, higher organic and inorganic pollution can be expected wherever these insecticides are present.

Microbial degradation of the debris may still occur, but it would be slower and produce undesirable by-products such as methane and sulfides Sorrell and Boon, ; Kwok et al. The combined impacts by neonicotinoids and other pollutants could gradually poison the surface waters in many parts of the world.

Thus, neonicotinoids do not cause fish mortality directly, but because aquatic invertebrates are a rich food source for many species of fish, depletion and disappearance of this source in waters contaminated with neonicotinoids could affect fish stocks in freshwater ecosystems. In the Netherlands, where residues of imidacloprid in water are the highest in the world Table S1 , correlations between such residues and the decline of arthropod taxa such as Ephemeroptera, Odonata, Diptera and some crustaceans have been found van Dijk et al.

Although not all the declines can be blamed on neonicotinoids, because other pesticide residues are also found and can have similar impacts Beketov et al.

As already mentioned, populations of aquatic species exposed to neonicotinoids often do not recover. This suggests that recovery of the extinct populations in the following year must require re-colonization from nearby areas. The elimination of predatory species results in the increase of prey species, with some of them, like mosquitoes Figure 6B , being a nuisance and a health hazard.

In agricultural areas treated extensively with seeds containing neonicotinoids the chances of re-colonization are less frequent for species that are not very mobile. Aquatic insects and invertebrate species are being removed from many land and water areas and heading toward extinction. This dire prediction is not far from the reality in some places.

Many of these flying insects have aquatic life cycles, and their disappearance is probably due to their larvae not having survived in water. This astonishing reduction in entomofauna parallels the decline of wild bee species in North America and the British Isles Fitzpatrick et al. It must be remembered that neonicotinoids were introduced in the early s. Many of the vertebrates living around rivers, lakes and ponds are insectivorous species that depend almost exclusively on aquatic invertebrates as their food source: frogs, newts, skinks and lizards, a large array of birds including passerines and waders, bats and shrews.

All these animals, whether terrestrial or amphibian, draw their food from flying insects, their aquatic larvae, crustaceans and worms that live in the water environment. Consequently, the depletion of this food source must necessarily affect them Tennekes, b.

To date, the only study available that makes a connection between bird declines and neonicotinoids in water was carried out in the Netherlands Hallmann et al. The authors of that study collected information on 15 species of passerine birds in that country over 20 years since , and correlated their abundance with residue concentrations of imidacloprid and other pesticide residues in water during the same period. All bird species studied were either insectivorous or fed insects and larvae to their offspring during the breeding season.

The only pesticide that explained the declining trends of 14 bird species was imidacloprid, whereas other factors that were taken into consideration, such as urban or agricultural area, availability of some cereal crops, fertilizer use and others, were discarded by the statistical analysis.

For the 6 species that showed a significant decline with imidacloprid residues, the average bird population decline was 3.

These levels are below the HC5 for imidacloprid 0. However, as demonstrated in the microcosm and mesocosm studies, they are sufficient to cause sublethal effects and delayed mortality, all of which can eliminate entire populations of invertebrates, without recovery in many cases.

Starvation by depletion of food sources due to pesticides was demonstrated for gray partridges Perdix perdix in England Potts, Also, applications of fipronil insecticide for locust control in Madagascar reduced the abundance of two species of tenrec, a skink and iguanian lizards that depended on termites as their main food source Peveling et al. Evidence of similar impacts by neonicotinoids on vertebrate taxa other than birds does not exist because of difficulties in obtaining relevant long-term experimental data.

However, if terrestrial birds, lizards and mammals can be taken as examples of what occurs in nature when pesticides reduce the food source, it is reasonable to think that other taxa that are experiencing worldwide declines, such as frogs and bats can be affected by indirect neonicotinoid impacts on the aquatic environment Mason et al.

Establishing the link between food depletion and population declines in some species is not difficult, but linking food depletion to individual chemical causes is a more challenging task. Negative impacts of neonicotinoids in aquatic environments are a reality. Initial assessments that considered these insecticides harmless to aquatic organisms may have led to a relaxation of monitoring efforts, resulting in the worldwide contamination of many aquatic ecosystems with neonicotinoids.

The decline of many populations of invertebrates, due mostly to the widespread presence of waterborne residues and the extreme chronic toxicity of neonicotinoids, is affecting the structure and function of aquatic ecosystems. Consequently, vertebrates that depend on insects and other aquatic invertebrates as their sole or main food resource are being affected. Declines of insectivore bird species are quite evident so far, but many other terrestrial and amphibian species may be at risk.

Solutions must be found soon if we are to save the biodiversity not only of aquatic ecosystems, but all other ecosystems linked by the food web. Since the prophylactic use of seeds treated with neonicotinoids is responsible for most of the soil and aquatic contamination, while there is evidence of little productivity gain, one obvious solution is to stop the marketing of seeds coated with these insecticides van der Sluijs et al.

At the same time, remediation systems based on photolytic processes Malato et al. All three authors contributed equally to the experimental data reviewed here. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Alexander, A. Effects of insecticide exposure on feeding inhibition in mayflies and oligochaetes. Emergent body size of mayfly survivors. Anderson, J. Neonicotinoids in the Canadian aquatic environment: a literature review on current use products with a focus on fate, exposure, and biological effects. Total Environ. Bajeer, M. Adsorption and leaching potential of imidacloprid pesticide through alluvial soil. Beketov, M. Pesticides reduce regional biodiversity of stream invertebrates.

Acute and delayed effects of the neonicotinoid insecticide thiacloprid on seven freshwater arthropods. Potential of 11 pesticides to initiate downstream drift of stream macroinvertebrates. Variability of pesticide exposure in a stream mesocosm system: macrophyte-dominated vs.

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Long-term stream invertebrate community alterations induced by the insecticide thiacloprid: effect concentrations and recovery dynamics. Bonmatin, J. Environmental fate and exposure; neonicotinoids and fipronil. Effects of low-dosed imidacloprid pulses on the functional role of the caged amphipod Gammarus roeseli in stream mesocosms. Brock, T. Macroinvertebrate responses to insecticide application between sprayed and adjacent nonsprayed ditch sections of different sizes.

Brown, A. Ecology of Pesticides. Cameron, S. Patterns of widespread decline in North American bumble bees. Plasma cholinesterase levels and health symptoms in Peruvian farm workers exposed to organophosphate pesticides.

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