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Combined effects of polystyrene nanoplastics and dinophysistoxin-1 (DTX1) on physiological performance of marine diatom Thalassiosira minima
Summary
Scientists studied how polystyrene nanoplastics and a marine algal toxin called dinophysistoxin-1 affect a common ocean diatom, both individually and in combination. The nanoplastics alone reduced diatom growth by over 50%, while the toxin reduced it by 22%, but when combined, the nanoplastics actually absorbed some of the toxin and partially offset its effects. The study suggests that nanoplastic pollution in coastal waters creates complex, unpredictable interactions with other marine contaminants that could disrupt the base of the ocean food chain.
Currently micro- and nanoplastics (MNPs) and microalgal toxins have become two typical groups of emerging contaminants in various coastal regions worldwide. However, the knowledge about their combined effects on marine organisms is still limited. This study explored the single and combined effects of polystyrene nanoplastics (PSNPs) at 50 mg L and dinophysistoxin-1 (DTX1) at 1 µmol L (819 μg l) on the diatom Thalassiosira minima. Results showed that the growth of T. minima was reduced by 22 ± 1.6 %, 53 ± 2.7 %, and 40 ± 2.8 % in DTX1, PSNPs, and their combined treatments, respectively. The maximum adsorption potential of DTX1 on PSNPs reached 78 % after 24 h, which might explain the antagonistic effect of PSNPs and DTX1 on growth and oxidative stress parameters. However, they demonstrated an additive effect on chlorophyll a biosynthesis, nitrogen assimilation, and the silicification of diatoms. The coupling of the silica to nitrogen (Si:N) uptake ratio in diatoms was significantly altered; extracellular dissolved inorganic nitrogen (DIN) in the treatment of PSNPs was reduced by 11.3 ± 4.1 %, while it increased by 47.9 ± 14 % and 60.4 ± 6.9 % in treatments with DTX1 and the combined treatment, respectively. Silicification of T. minima was reduced by 50 ± 5.9 % and 49 ± 1.8 % in treatments with DTX1 alone and the combined treatment, respectively. These findings suggest that DTX1 exposure results in an increase in N uptake and a decrease in Si uptake, demonstrating an inverse effect on the uptake of nutrients. Transcriptome analysis revealed downregulation of some amino acid genes possibly accounts for this change. This study is significant for understanding the combined effects of microplastics and phycotoxins on diatoms.