Comprehensive characterization of the acute and chronic toxicity of the neonicotinoid insecticide thiamethoxam to a suite of aquatic primary producers, invertebrates, and fish

Abstract

Thiamethoxam is a neonicotinoid insecticide used widely in agriculture to control a broad spectrum of chewing and sucking insect pests. Recent detection of thiamethoxam in surface waters has raised interest in characterizing the potential impacts of this insecticide to aquatic organisms. We report the results of toxicity testing (acute and chronic) conducted under good laboratory practices for more than 30 freshwater species (insects, molluscs, crustaceans, algae, macrophytes, and fish) and 4 marine species (an alga, a mollusc, a crustacean, and a fish). As would be anticipated for a neonicotinoid, aquatic primary producers and fish were the least sensitive organisms tested, with acute median lethal and effect concentrations (LC50/EC50) observed to be !80 mg/L in all cases, which far exceeds surface water exposure concentrations. Tested molluscs, worms, and rotifers were similarly insensitive (EC50 ! 100 mg/L), except for Lumbriculus sp., with an EC50 of 7.7 mg/L. In general, insects were the most sensitive group in the study, with most acute EC50 values < 1 mg/L. However, the crustaceans Asellus aquaticus and Ostracoda exhibited a sensitivity similar to that of insects (acute EC50 < 1 mg/L), and the midge larvae Chaoborus sp. were relatively insensitive compared with other insects (EC50 > 5.5 mg/L). The most sensitive chronic response was for Chironomus riparius, with a 30-d no-observed-effect concentration (NOEC; emergence) of 0.01 mg/L. Observed toxicity to the tested marine organisms was comparable to that of freshwater species. We used the reported data to construct species sensitivity distributions for thiamethoxam, to calculate 5% hazard concentrations (HC5s) for acute data (freshwater invertebrates), and compared these with measured concentrations from relevant North American surface waters. Overall, based on acute toxicity endpoints, the potential acute risk to freshwater organisms was found to be minimal (likelihood of exceeding HC5s < 1%).

Acute toxicity of 6 neonicotinoid insecticides to freshwater invertebrates

“…When compared with neonicotinoids in North American surface water samples, the risk was found to be low, with a likelihood of ∼0.5% of exceeding the HC5. In contrast to these studies, an earlier assessment by Morrissey et al derived an HC5 of 0.63 μg L − 1 , which is lower than the results shown in the present study and by others (Finnegan et al ; Whitfield‐Aslund et al ).…”

“…A recent probabilistic ecological risk assessment for imidacloprid by Whitfield-Aslund et al (2017), which considered both acute lethal and immobility data, derived an acute HC5 of 1.73 mg active ingredient L À1 ; when compared with exposure distributions for multiple use patterns, they categorized the risk to aquatic invertebrates as de minimis. Similarly, Finnegan et al (2017) constructed an acute SSD for thiamethoxam and derived HC5s of 5.1 and 22.9 mg L À1 using EC50s and LC50s, respectively. When compared with neonicotinoids in North American surface water samples, the risk was found to be low, FIGURE 2: Species sensitivity distributions (SSDs) of acute ( 5 d) toxicity data for 6 neonicotinoids constructed using median lethal concentration (LC50) values for aquatic invertebrates generated from the present study and external literature data mined from the ECOTOX database.…”

Effects of neonicotinoids on putative escape behavior of juvenile wood frogs (Lithobates sylvaticus) chronically exposed as tadpoles

“…Such differences are evident with neonicotinoids: both our study and that of Crosby et al (2015) found significant effects, but others did not (Finnegan et al 2017;Miles et al 2017). No sublethal effects on swimming behavior, feeding activity, or reactions to an external stimulus were detected during acute and chronic exposures of rainbow trout (Oncorhynchus mykiss) to thiamethoxam (maximum concentration tested was 100 mg/L; Finnegan et al 2017). No sublethal effects on swimming behavior, feeding activity, or reactions to an external stimulus were detected during acute and chronic exposures of rainbow trout (Oncorhynchus mykiss) to thiamethoxam (maximum concentration tested was 100 mg/L; Finnegan et al 2017).…”

Modeling the effects of thiamethoxam on Midwestern farm ponds and emergent wetlands

“…The reference Ashwell and Dark (2002) a Acute and chronic endpoints were based on evaluation of data summarized by Finnegan et al (2017). Average daily biomass for the diatoms ranged from 0.05 to 4.47 g C/m 2 .…”