In the ocean plastic does not naturally biodegrade but breaks down into ever smaller pieces. Plastics in the ocean cause (potential) harm to the health of people and animals in a number of different ways.
- Plastic as (toxic) food
Animals are not always able to distinguish plastic from food. Organisms that filter water (plankton, shellfish, sperm whales) or that live in the sand (sandworms) certainly can’t make the difference. Some fish view small plastic particles as fish eggs and target the floating plastic. Turtles can confuse plastic bags with jellyfish. Plastic is regularly found in the stomachs of the fulmar, which forages with open beak just above the water’s surface. On land many grazing animals also ingest plastic.
Animals that ingest relatively large pieces of plastic can starve to death if the plastic blocks their intestines. Think of a plastic bag or balloon. In such cases an animal can perish fast. Sometimes their beaks or mouths are larger than their anus and plastic can accumulate. Dozens of pieces of plastic are regularly found in the stomachs of seabirds, turtles or whales. Well known are the terrible photos of young albatross on Midway being fed plastic by their parents.
When animals ingest plastic, it can lead to a reduction of proper intestinal function resulting in the inability to digest real food. Furthermore the plastic can over stimulate the immune system. The body responds as if dealing with infection. Plastic drains the animals’ energy for which they get nothing in return.
Plastics (but not only plastics) have the property to act like a sponge for certain toxins (Persistent Organic Pollutants, POPs) such as polychlorobifenyl (PCBs) and polycyclic aromatic hydrocarbons (PAHs). This concerns the five most produced plastics, amongst which polyethylene (PE), polyethyleneterephtalate (PET) en polyvinylchloride (PVC). The longer the plastic stays in the water, the more toxic it becomes through the sponge effect. Animals that ingest this toxic plastic, do generally excrete it as well. An important scientific question is whether toxic chemicals accumulate in their body tissue and will, through bioaccumulation, end up higher in the food chain. Humans are at the top of the food chain.
Japanese researchers have found poly bromodifenyl ether (PBDE), a flame retardant added to plastic, in the tissue of some seabirds. This chemical can’t originate from their natural pray, but must have come from ingested plastic. According to researchers this can be an indication that toxic chemicals that have been ingested can be absorbed into the body tissue of seabirds.
The smallest plastics (nanoplastics) can pass through cell walls and thus migrate in theory from the digestive system to the body tissue of humans and animals.
Animals can get entangled in plastic and die as a consequence. Fishnets and abandoned fishnets (so called ghost nets) have many victims. Mammals (like dolphins and seals) can’t stay under water for long and die quickly. Birds can also get entangled in plastic, for example in balloon strings.
- Leaching of additives
Additives to plastic can be harmful for the environment when these substances leach from the plastic and end up in the environment or food chain. This is a (daily) problem with the use of plastic. Additives that leach from plastic in the ocean are immediately diluted through which levels of concentration are no longer measurable. In the ocean the leaching of these chemicals is fairly insignificant. However it is significant on land. On this theme, see for instance this American documentary from 2009:
The best known and most controversial is bisphenol A (BPA). BPA is found in many types of plastic, i.e. packaging such as plastic bottles. It concerns unbreakable plastic that is easy to clean. Under certain conditions (damage or heating) BPA can be released and end up in food. The chemical acts as a hormone, in particular the female hormone estrogen. Even small amounts are said to have harmful effects. It could explain today’s children reaching puberty at a younger age. In June 2011 a ban was introduced in Europe on the sale of baby bottles containing bisphenol A.
Despite the concerns BPA is still processed in plastic on a large scale. Most of the BPA production is for the manufacture of polycarbonate, a strong and transparent plastic that can be identified with the recycle code #7.
Phtalates are used as softeners for plastic (especially in polyvinylchloride, PVC). Because the phtalate softener molecules move between the polymer chains that are the building blocks of plastic, a part of these softeners escape over time and end up in the environment. There, the phtalates don’t break down completely. They can accumulate in small organisms and subsequently end up in the food chain. Research has shown that phtalates disturb the hormonal balance of people and animals and have carcinogenic properties.
Plastic is made of petroleum and that burns well. To prevent plastic from burning easily flame retardants are added. Much use is made in synthetics of organobromine compounds such as PBB’s (polybrominated-bifenyl) en PBDE’s (polybrominated diphenyl ethers). The retardants are amongst other processed in the following types of plastic polystyrene (PS), polyurethane (PUR), polyvinylcholoride (PVC) en polypropelyne (PP). These plastics are toxic and don’t easily break down. When burnt flame retardants release toxic dioxins.
Formaldehyde can be released from MF (melamine-formaldehyde). Formaldehyde is also applied in some plastic bottles and packaging plastics. The chemical has been classified as carcinogenic. Exposure can lead to irritation of eyes, nose, throat or skin. Some people are allergic to formaldehyde.