Do microplastic particles affect Daphnia magna at the morphological, life history and molecular level?

Microplastic particles are ubiquitous not only in marine but also in freshwater ecosystems. However, the impacts of microplastics, consisting of a large variety of synthetic polymers, on freshwater organisms remains poorly understood. We examined the effects of two polymer mixtures on the morphology, life history and on the molecular level of the waterflea Daphnia magna (three different clones). Microplastic particles of similar to 40 mu m were supplied at a low concentration (1% of the food particles) leading to an average of similar to 30 particles in the digestive tract which reflects a high microplastic contamination but still resembles a natural situation. Neither increased mortality nor changes on the morphological (body length, width and tail spine length) or reproductive parameters were observed for adult Daphnia. The analyses of juvenile Daphnia revealed a variety of small and rather subtle responses of morphological traits (body length, width and tail spine length). For adult Daphnia, alterations in expression of genes related to stress responses (i.e. HSP60, HSP70 & GST) as well as of other genes involved in body function and body composition (i.e. SERCA) were observed already 48h after exposure. We anticipate that the adverse effects of microplastic might be influenced by many additional factors like size, shape, type and even age of the particles and that the rather weak effects, as detected in a laboratory, may lead to reduced fitness in a natural multi-stressor environment

Moving Toward Standardized Toxicity Testing Procedures with Particulates by Dietary Exposure of Gammarids

Ecotoxicological effect assessment of particulate materials and sparingly soluble substances is an emerging field. Current standard toxicity tests of aquatic organisms are based on soluble substances which are added to the aqueous phase. Although soluble substances distribute homogeneously, particles can form aggregates, resulting in inhomogeneous distribution and unpredictable exposure. Therefore, test scenarios need to be adapted to overcome these uncertainties. We present a dietary particle exposure tool for the toxicity testing of sparingly soluble substances or particles in combination with a standardizable food source for gammarids based on decomposition and consumption tablets (DECOTABs). Four food supplements in the DEOCOTAB formulation were compared to test their influence on the energy reserves of gammarids. Although feeding rate was constant for most supplements, mortality and energy reserves revealed clear differences. Tabs supplemented with algae‐based phyll or animal protein–based trout food best met all of the requirements. Fluorescent plastic microparticles (10–65 µm) were homogenously distributed and stable in the DECOTABs. Constant feeding was observed, and the number of ingested microparticles by Gammarus roeseli was quantified in relation to the consumed food. The developed method provides a realistic and methodologically reliable uptake from the oral pathway and allows the quantification of inner exposition via feeding rate, providing a promising tool for standardized dietary exposure scenarios with particles. Environ Toxicol Chem 2021;40:1463–1476. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.Bayerische Forschungsstiftung http://dx.doi.org/10.13039/501100002745Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/50110000234

Morphological parameters of juvenile <i>D</i>. <i>magna</i>.

<p>Body length, body width and tail spine length clones Bl2.2, K34J and Max 4. The statistical analyses of body width and tail spine length were performed using body length as a covariate in order to compensate for size-dependent differences and by nesting the five individuals of each replicate. Likewise for the figures body width and tail spine length were drawn as relative values of the body length in percent. The five individuals of each replicate were averaged to represent the nested individuals in the graphs. Error bars indicate the 95% confidence intervals. Significance level against the control treatment is indicated by * p<0.05, ** p<0.01.</p

Experimental set-up for each of the three <i>D</i>. <i>magna</i> clones.

<p>1) Initially, 20 primiparous <i>Daphnia</i> (6 replicates per clone and treatment) were cultured without any plastic particles. 2) When the animals reached primiparity, they were transferred to a glass jar prepared 24h prior with fresh artificial medium, food and the corresponding plastic mixtures. 3) They were exposed to their respective treatments for over 48 hours. 4) After the exposure, 15 of the <i>Daphnia</i> of each replicate were preserved for (I) gene expression analyses (6 replicates per treatment). 5) From the remaining five animals, three were transferred individually into small glass jars (18 replicates per treatment). These were cultured until they produced the 5^th brood for assessing (II) morphology and life-history parameters.</p

Morphological parameters of adult <i>D</i>. <i>magna</i>.

<p>Body length, body width and tail spine length of the clones Bl2.2, K34J and Max 4; measured 48h after primiparity and upon carrying the 3^rd and 5^th clutch. Statistical analyses of body width and tail spine length were performed using body length as a covariate in order to compensate for size-dependent differences. Likewise, for the figures body width and tail spine length were drawn as relative values of the body length in percent. Error bars indicate the 95% confidence intervals. Significance level against the control treatment is indicated by * p<0.05, ** p<0.01.</p

Do microplastic particles affect <i>Daphnia magna</i> at the morphological, life history and molecular level? - Fig 2

<p><b>Expression profile of <i>D</i>. <i>magna</i> clone BL2.2, K34J and Max4 after 48h exposure to plastic mix A and B.</b> Reference genes used for normalization of gene expression were for BL2.2: SDH, TBP and UBC; for K34J: GAPDH and UBC and for Max4: STX16, UBC and GAPDH. Error bars indicate 95% confidence interval. Confidence intervals are not affected by the correction for multiple testing by the false discovery rate method. * p<0.05, ** p<0.01.</p