Ingestion of micro- and nanoplastics in Daphnia magna - Quantification of body burdens and assessment of feeding rates and reproduction.

TLDR: The lower egestion and decreased feeding rates, caused by the 100 nm particles, could indicate that particles in the nanometer size range are potentially more hazardous to D. magna compared to larger particle sizes.

About: This article is published in Environmental Pollution.The article was published on 2017-09-01 and is currently open access. It has received 300 citations till now. The article focuses on the topics: Particle size.

Figures

Fig. 2. Body burdens of particles (mass/animal) for Daphnia magna (1 week old) after 24 h ingestion (in particle suspensions of 1 mg/l) and 24 h egestion (in clean medium) of 100 nm (top) and 2 µm (bottom) polystyrene particles with or without the presence of algae in the medium. Groups that do not share the same letter are significantly different from each other.

Fig. 1. Body burdens of particles (mass/animal) for Daphnia magna (1 week old) exposed to 100 nm (round symbols) and 2 µm (triangular symbols) polystyrene particles during a 24 h ingestion phase (closed symbols) in a particle suspension of 1 mg/l, followed by a 24 h egestion phase (open symbols) in clean medium. The mean and standard deviation for the 3 replicates per sampling point are shown.

Fig. 4. Number of neonates produced per mother animal within the 21 days reproduction test, in which animals were exposed to 100 nm or 2 µm polystyrene particles at different concentrations (0.1 mg/l. 0.5 mg/l, 1 mg/l). Groups that do not share the same letter are significantly different from each other.

Table 3 Results of the two-factorial ANOVA of the body burden after 21 days exposure to 100 nm and 2 µm particles including the degrees of freedom (d.f.), the mean squares (MS), the F-ratios and P-values.

Fig. 3. Body burdens of particles (mass/animal) for Daphnia magna at the end of the 21 days reproduction test, in which animals were exposed to 100 nm or 2 µm polystyrene particles at different concentrations (0.1 mg/l. 0.5 mg/l, 1 mg/l). Groups that do not share the same letter are significantly different from each other.

Table 1 Results of the two-factorial ANOVA of the body burden of 100 nm and 2 µm particles (factor ‘size’) during a 24 h ingestion or egestion phase in the presence or absence of food (factor ‘sampling phase’); including the degrees of freedom (d.f.), the mean squares (MS), the F-ratios and P-values.

Frequently asked questions

Q1. What are the contributions in "Ingestion of micro- and nanoplastics in daphnia magna – quantification of body burdens and assessment of feeding rates and reproduction" ?

The aim of this study was therefore to use a quantitative approach for determining ingestion and egestion of microand nanoplastics in Daphnia magna and to analyze the influence of particle size, exposure duration and the presence of food. Both particle sizes were readily ingested, but the ingested mass of particles was five times higher for the 2 μm particles than for the 100 nm particles. Complete egestion did not occur within 24 h but generally higher amounts of the 2 μm particles were egested. Daphnid feeding rates decreased by 21 % in the presence of 100 nm particles, but no effect on reproduction was found despite high body burdens of particles at the end of 21 days exposure. The lower egestion and decreased feeding rates, caused by the 100 nm particles, could indicate that particles in the nanometer size range are potentially more hazardous to D. magna compared to larger particle sizes. Furthermore, feeding rates of daphnids in response to particle exposure were measured as well as effects on reproduction during a 21 days exposure ( at 1 mg/l, 0. 5 mg/l and 0. 1 mg/l ) to investigate potential impairments of physiology. 

Q2. How long did the animals have to be rinsed?

After sampling, the animals were rinsed with deionized water for approximately half a minute to remove all plastic particles from the surface. 

Q3. What was the mechanism of selective feeding of phytoplankton over clay particles?

Kirk (1991) found selective feeding of phytoplankton over clay particles, which was described as passive selectivity since the animals capture them less efficiently instead of actively rejecting the inorganic particles. 

Q4. What software was used to do the graphs and statistical analyses?

All graphs and statistical analyses were done with the free statistical computing software R (version 3.2.5 (2016-04-14)) (R Core Team, 2016). 

Q5. What is the reason for the higher body burdens of the smaller particles?

Smaller particles may for instance agglomerate to a larger degree in the presence of algal and animal exudates, which could increase their availability to daphnids (Nasser and Lynch, 2016). 

Q6. What was the effect of the particle size on the egestion of D. magna?

A faster depuration in the presence of food was observed and the residual concentrations were dependent on particle size and higher for the bigger particles (30 nm in contrast to 10 nm). 

Q7. What factors were used to determine the effect of food presence in the ingestion/egestion test?

The effect of food presence in the ingestion/egestion test (experiment 2) was analyzed using a two-factorial ANOVA with the factors ‘sampling phase’ and ‘size’. 

Q8. What was the average body burden for the 100 nm particles?

After the 24 h ingestion phase without the addition of food, average body burdens were 0.23 µg/animal for the 100 nm particles and 1.3 µg/animal for the 2 µm particles (Fig. 2). 

Q9. What is the way to measure the particle amount?

Another possibility as described by Rosenkranz et al. (2009) is to measure fluorescence intensity as a proxy for the particle amount. 

Q10. What tests were used to check the normality of residuals?

Additionally the normality of residuals was tested with the Shapiro-Wilks-W-Test and the homogeneity of variances with the Fligner-Killeen Test. 

Q11. What was the method to measure the fluorescence of a series of different particles?

In order to deduct the particle quantity from the fluorescence measurement, a standard curve correlating particle concentration and fluorescence was made for each particle size. 

Q12. How much weight was found to be reduced in the group exposed to 100 nm particles?

In the group exposed to 100 nm particles the feeding rate was found to be significantly lower than in the control group (p=0.013) with a reduction of 21%.