Abstract
Microplastics (MP) widely distributed in aquatic environments have adverse effects on aquatic organisms. Currently, the impact of MP on toxigenic red tide microalgae is poorly understood. In this study, the strain of Alexandrium pacificum ATHK, typically producing paralytic shellfish toxins (PST), was selected as the target. Effects of 1 and 0.1 μm polystyrene MP with three concentration gradients (5 mg L−1, 25 mg L−1 and 100 mg L−1) on the growth, chlorophyll a (Chl a), photosynthetic activity (Fv/Fm) and PST production of ATHK were explored. Results showed that the high concentration (100 mg L−1) of 1 μm and 0.1 μm MP significantly inhibited the growth of ATHK, and the inhibition depended on the size and concentration of MP. Contents of Chl a showed an increase with various degrees after MP exposure in all cases. The photosynthesis indicator Fv/Fm of ATHK was significantly inhibited in the first 11 days, then gradually returned to the level of control group at day 13, and finally was gradually inhibited in the 1 μm MP treatments, and promotion or inhibition to some degree also occurred at different periods after exposure to 0.1 μm MP. Overall, both particle sizes of MP at 5 and 25 mg L−1 had no significant effect on cell toxin quota, and the high concentration 100 mg L−1 significantly promoted the PST biosynthesis on the day 7, 11 and 15. No significant difference occurred in the cell toxin quota and the total toxin content in all treatments at the end of the experiment (day 21). All MP treatments did not change the toxin profiles of ATHK, nor did the relative molar percentage of main PST components. The growth of ATHK, Chl a content, Fv/Fm and toxin production were not affected by MP shading. This is the first report on the effects of MP on the PST-producing microalgae, which will improve the understanding of the adverse impact of MP on the growth and toxin production of A. pacificum.
Highlights
Plastic products have been widely used in daily life due to the characteristics of light weight, strong plasticity, insulation and low cost
In the exposure treatments of 1 μm MP, the growth of ATHK was significantly inhibited by 21% to 55% during the entire growth cycle in 100 mg L−1 treatment group compared to the control group (Figure 3), while it was less affected in other concentrations of MP treatments
The inhibition rate of ATHK exposed to 1 μm MP reached a maximum of 55% in the 100 mg L−1 group on the third day of growth and decreased to 21% when they grew on day 21, while their density in the 5 and 25 mg L−1 groups was similar as in the control group on day 21
Summary
Plastic products have been widely used in daily life due to the characteristics of light weight, strong plasticity, insulation and low cost. The amount of plastic litter in aquatic and terrestrial environments has increased dramatically over the past few decades [2]. These plastic wastes are fragmented and disintegrated into ubiquitous and long-lasting small microplastics (MP) through physical, chemical and biological processes such as weathering, seawater erosion and biodegradation. MP are widely distributed in marine environment, from surface seawater to sediments [5,6], and from the Artic to the Antarctic [7,8], as well as in freshwaters [9], such as rivers or lakes
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