Genetic and Physiological Damage Caused by Nanoplastics in Mussels: First-Time Observation

Researchers exposed the mussels, which originated from the Portuguese coast, to the presence of polystyrene nanoplastics during four days, in concentrations ranging from 0.005 milligrams per litre up to 50 milligrams per litre, and detected variations in the expression of several genes in the gills and digestive glands. A concentration of 0.05 mg per litre (mg/L) was sufficient for changes to be observed in the expression of these genes. This concentration modifies the activity of the cat (cathepsin) gene, related to the correct functioning of the immune system in the mussel’s gills. With 0.5 mg/L of nanoplastics, the cyp11 gene – related to the biotransformation of chemical substances for the correct functioning of the organism – also expressed itself in excess in the gills. And with 5 mg/L, the expression of both the cyp32gene, related to biotransformation, and the lys gene, related to the immune system, was affected. Higher concentrations (50 mg/L) modified the expression of the hsp70 gene, related to cell-tissue repair, in the digestive glands of mussels.

Researchers also were able to observe how nanoplastics can heighten the toxic effects of other contaminants. Among the most common contaminants absorbed by nanoplastics is carbamazepine, a drug that treats seizure disorders. Adding small concentrations (6.3 micrograms per litre) of this drug to the presence of nanoplastics creates an increase in absorption when compared to the drug by itself. The combination of carbamazepine with only 0.05 mg/L of nanoplastics modified the expression of tumour suppressor p53, related to DNA damage repair, in addition to the expression of the aforementioned genes cyp32, hsp70 and lys.

Researchers also observed the physiological effects of nanoplastics starting with only 0.005 mg/L. At this level of concentration the nanoplastics already produced alterations in the activity of the gill’s alanine transaminase (ALT), while with 0.05 mg/L damage could be seen in the DNA of the haemolymph (the “blood” of molluscs), in cell membranes, and alterations in the biochemical indicators related to oxidative stress both in gills and in the digestive glands.