Microplastics: An Unsafe Pathway from Aquatic Environment to Health—A Review

Abstract

Waste is considered to be any solid material that is manufactured or processed and then discarded or disposed, ending up either in a terrestrial or an aquatic environment. It is possible to curb the negative effects of waste when it is dumped on land, but as it enters water, its potential impact is unpredictable, as water is a universal solvent with an ability to dissolve and hoard contaminants. Contaminants can be organic and inorganic, which determine their associated toxicity. Various solid wastes such as plastic, glass, metal, rubber, and wood have already polluted available potable water resources. Of all contaminants, plastics are commonly used presently and although they reduce the exploitation of natural resources, they are highly persistent in nature and end up in water bodies in the form of plastic debris. Plastic debris within an aquatic environment can be macro, meso, micro, or nano in size. Larger macro-size particles have been reported to commonly entangle aquatic invertebrates, birds, mammals, and turtles. On the other hand, micro- and nano-size particles form through different fragmentation processes such as photodegradation and microbial degradation, and as a result of other external forces. Micro-sized plastics (<5 mm in diameter) are ubiquitous in water, sediment, and their associated biota. Their smaller size and colorful appearance makes them resemble food for aquatic organisms, and hence they bioaccumulate easily. Also, additives used during plastic synthesis are released into the aquatic and terrestrial environments in the form of toxic chemicals. Among anthropogenic “cosmetics,” toothpaste is considered to be one of the major contributors to microplastics pollution. It uses micro-sized beads for exfoliation. Research on microplastics is rapidly increasing worldwide, and microplastics have already been tagged as an alarming threat, but there exists a knowledge gap on actual concentrations, their impacts, and their sources. This review addresses possible types and sources of microplastics, their bioavailability, and an analysis of their fate, or potential impact, on aquatic environments.