Acute sensitivity of three Cladoceran species to different types of microplastics in combination with thermal stress

Abstract

Microplastics (<5 mm, MP) are ubiquitously distributed in the environment, causing increasing concern regarding their potential toxicity to organisms. To date, most research has focussed on the impacts of MPs on marine and estuarine organisms, with fewer studies focussing on the effects of microplastics on freshwater ecosystems, especially under different environmental conditions. In the present study, the sensitivity of two temperate Cladoceran species, Daphnia magna and Daphnia pulex, and a smaller tropical species Ceriodaphnia dubia, to primary microplastics (PMP) and secondary (weathered) microplastics (SMP) was assessed. A prolonged acute toxicity assay (up to 72 or 96 h) was performed at 18°, 22°, and 26 °C, to determine the influence of temperature as an additional stressor and survival data were analysed using toxicokinetic-toxicodynamic (TK-TD) model. Acute sensitivity of D. magna and D. pulex to both PMP and SMP increased sharply with temperature, whereas that of C. dubia remained relatively stable across temperatures. C. dubia was the most sensitive species at 18 °C, followed by D. pulex and D. magna, which were of comparable sensitivity. However, this ranking was reversed at 26 °C as could be seen from the No Effect Concentration (NEC) estimates of the TK-TD model. In addition, SMP and PMP had a similar effect on D. magna and D. pulex, but PMP was more toxic to C. dubia. Effects on survival were strongly time-dependent and became substantially more severe after the standard 48 h test period. Our results indicate that sensitivity to microplastics may differ between species for different types of microplastics, and could be drastically influenced by temperature albeit at high exposure concentrations.

Reproductive toxicity of primary and secondary microplastics to three cladocerans during chronic exposure

“…This variation in species sensitivity may be inversely correlated with their body size (D. magna: D. pulex: C. dubia e 4.5:3:1 approximately) and therefore body volume. This is in line with previous studies comparing chemical toxicity of species with different body sizes, reporting the inverse correlation of sensitivity with body volume to copper nanoparticles, zinc, and microplastics (Song et al, 2015;Vesela and Vijverberg, 2007;Jaikumar et al, 2018). The metabolic rates of smaller sized species are higher than that of larger species (Vesela and Vijverberg, 2007).…”

“…We previously assessed the acute toxicity of PMP and SMP on the same three species (Jaikumar et al, 2018) and reported that at 18 C, species under study showed a similar acute sensitivity distribution as demonstrated in the present study (C. dubia > D. magna ! D. pulex).…”

“…Briefly, polyethylene microspheres (850e1000 mm, 0.96 g/cm 3 ; Cospheric LLC, Goleta, USA) were ground (Retsch CryoMill; Retsch, Dusseldorf, Germany), and subsequently sieved to yield irregular and coarse particles, as a model for SMP. The size range of these particles was 1e10 mm (validated using TEM; see Jaikumar et al, 2018). Next, the particles were suspended using the surfactant Tween 80 (Sigma Aldrich), followed by serial centrifugation with Milli-Q water to remove the surfactant (Jaikumar et al, 2018).…”

“…The size range of these particles was 1e10 mm (validated using TEM; see Jaikumar et al, 2018). Next, the particles were suspended using the surfactant Tween 80 (Sigma Aldrich), followed by serial centrifugation with Milli-Q water to remove the surfactant (Jaikumar et al, 2018). Finally, stock suspensions were prepared using Elendt M4 medium (10 7 p/mL), and further desired exposure concentrations were achieved through serial dilution.…”

“…In a recent study, Ogonowski et al (2016) compared the toxicity of PMP and artificially weathered SMP on processes like feeding, growth as well as reproduction, during chronic exposure to D. magna and found that while PMP had limited impacts, exposure to SMP resulted in reduced reproductive output. Further, in an expansive study, we compared the sensitivity of three different Cladocerans during acute exposure to different types of microplastics in combination with thermal stress (Jaikumar et al, 2018), finding species-dependent sensitivity. However, such cross-species comparison of species sensitivity to differently shaped microplastics during chronic exposure has not been performed as of yet.…”