Microplastics in the Marine Environment

Plastic litter in the oceans is a global problem. Perhaps most noticeable to people are the large items of plastic litter washed up on beaches. In fact, it is so common on beaches that sadly many people may simply accept it as a normal feature of beaches today. However, while large plastic objects are the most visible, microplastics are the most common type of plastic in the ocean and therefore also on beaches. Microplastics can include the breakdown products of larger plastic objects or arise from sources such as cosmetic microbeads or the microfibres shed by your clothes every time they are washed. Microplastics measure less than 5 mm in size and consequently, many microplastics are largely invisible to the naked eye. For example, a microfiber is less than 0.01 mm (10 µm) in diameter and so just 1/5 the diameter of a human hair.

Dr. Richard Kirby is studying the plankton food web and how we influence it by climate change, fishing and plastic pollution.

Large plastic items in the sea, such as plastic bags, cigarette lighters, plastic bottles, and rope can be lethal to marine life when animals such as whales, seals, sea birds, and fish become entangled or mistake the rubbish for food. The small size of microplastics, however, means this plastic can affect the very base of the marine food chain in a similar fashion, when planktonic organisms become entangled (see video 1) or eat the plastic with lethal consequences (see video 2). Once microplastics have entered at the bottom of the food chain, they can then be passed upwards when the plankton are eaten by fish and the fish in turn by their predators, and so on. As plastics can also carry toxins on their surface, this provides a mechanism for the potential bioaccumulation of toxins upwards through the marine food chain.

While large plastic debris is easy to see, a recent study (Cozar A et al. (2014) Plastic debris in the ocean  Proc. Natl. Acad. Sci.  111  10239-10244) estimated that 99% of plastic remains unaccounted for in the ocean. In other words, we don’t know where it is. As microplastics can have consequences for the plankton and the marine food chain, it is clear that we need to know much more about the extent of microplastic pollution, and here, observation is a key first step to our understanding.