The effect of single and combined microplastics with heavy metals Cu and Pb on digestive enzymes in Paphia undulata

Abstract The contaminant most frequently found in aquatic habitats and potentially harms living things is called microplastic (MPs). MPs can also interact with other pollutants, such as heavy metals. This study aims to investigate the effects of PS particle of different sizes (20 and 150 µm) on the digestive enzymes (protease, amylase, and lipase) of the hard clam Paphia undulata, either alone or in combination with two distinct heavy metals (copper/Cu and lead/Pb). According to this study, clams' digestive enzyme responses often increased from days 5 to 7, then dropped the next day until the observation's completion. Greater enzyme activity results from exposure to larger particles (150 µm) than from smaller ones (20 µm). When heavy metals and MPs particles were exposed together, the peak phase of digestive enzyme activity was significantly higher (p < 0.05) than when only one particle or heavy metal was present. Hard clams exposed to MPs in combination with Pb increased digestive enzyme activity more than those exposed to MPs in combination with Cu. In addition, when PS particles were combined with Pb metal instead of Cu metal, the activity of digestive enzymes changed more quickly in the exposed clams. Clams exposed to PS in combination with Cu showed an increase in digestive enzyme activity on the seventh day of treatment, except for amylase. However, those treated with PS in combination with Pb metal showed an increase on the fifth day of exposure. This study demonstrates how these contaminants harm hard clams by disrupting their digestive systems, which can lead to growth inhibition and even death.