Section II: Plastics in the Environment
Microplastics and Nanoplastics in the Environment
M. Humam Zaim Faruqi and Faisal Zia Siddiqui CONTENTS
- 3.1 Introduction 47
- 3.2 Sources of Microplastics 49
- 3.2.1 Primary Microplastics 49
- 3.2.2 Secondary Microplastics 50
- 3.3 Microplastics Sampling and Abundance 50
- 3.3.1 Sampling Techniques 50
- 188.8.131.52 Beachcombing 51
- 184.108.40.206 Sediment Sampling 51
- 220.127.116.11 Marine Trawls 51
- 18.104.22.168 Marine Observational Surveys 51
- 22.214.171.124 Biological Sampling 51
- 3.3.2 Spatial and Temporal Variation of Microplastics 52
- 3.4 Fate of Microplastics and Nanoplastics in the Environment 53
- 3.4.1 Tracking the “Missing” Plastic 53
- 126.96.36.199 Nanofragmentation 53
- 188.8.131.52 Biofouling 53
- 184.108.40.206 Marine Ingestion 54
- 3.4.2 Interaction of Chemical Pollutants with Microplastics 54
- 3.5 The Way Forward 55
The term “plastic” is derived from the ancient Greek word plastikos, which refers to something that is appropriate for molding, and the Latin term plasticus, which means molding or shaping. The advent of plastics has led to fundamental transformation in the quality of human life and has facilitated unprecedented technological advancements. Because of its use in diverse sectors such as construction, packaging, transportation, healthcare and electronics, the development of this versatile and ubiquitous class of materials is widely perceived as one of the greatest technological achievements of the 21st century. Plastics are composed of large chain-like macromolecules which further consist of many recurring smaller molecules connected in a sequence. A substance with this kind of molecular arrangement is known as a “polymer.” Every individual molecule in a polymer chain is a single unit and is known as a “monomer.” Thus, monomers are small molecules that possess the ability to bond together to form long chains. A vast majority of polymers in today’s world are synthetic plastics. However, many natural polymers such as deoxyribonucleic acid (DNA) also exist. Therefore, it is important to note that although all plastics are polymers, not all polymers are plastics .
The global production of plastics increased 20-fold from 15 million tonnes (MT) in 1964 to about 335 MT in 2016 [2,67]. The production is further expected to double again in the next 20 years and quadruple by 2050 . Asia produced nearly half of the world’s plastic in 2014. China and Japan, with 26% and 4% of the global plastic production, respectively, are two of the highest plastic producers in Asia . About 50% of the produced plastics are utilized for single-use disposable applications, such as packaging, agricultural films and consumer items; 20%-25% for long-term infrastructure such as pipes, cable coatings and structural materials and the remainder for durable consumer applications such as electronic goods, furniture, vehicles, etc. . The increasing consumption of plastics can be attributed to the low cost, ease of handling and good durability of plastic material. Unfortunately, the growing demand of plastic products to advance our lifestyle has trapped us into a vicious cycle of producing, consuming and disposing them. The huge plastic waste generated worldwide indicates their widespread use in the urban settlements. However, the quantities of plastics that are reused or recycled are significantly low. The global rate of recycling of plastics across developed countries is about 17%, which is far lower than that of paper (58%) and iron and steel (70%—90%) [1,4,5]. In 2012, only about 6 MT (26%) and 2.5 MT (9%) of post-consumer plastics were recycled in the European Union (EU) and US, respectively. However, more than 8.75 MT of plastic in the EU and 29 MT in the US was discarded without recycling. The likely reason for this is the increase in manufacturing costs by about 20% when using recycled plastics, as opposed to utilizing virgin-plastic feedstock . Further, the repeated melting and molding of a normal commodity plastic also results in diminished mechanical properties and reduced durability.
Other than the plastic waste which is recycled, most of the plastic ends up in landfills, where it takes a few hundred years to decompose . However, a significant proportion of plastics end up unaccounted for in the environment and get deposited in terrestrial and marine ecosystems. While the dumping of plastics in terrestrial ecosystems occurs mainly from littering or illegal land disposal, plastic items end up as marine debris owing to littering, insufficient treatment capacity, transport by wind or surface runoff, illegal discharges of domestic and industrial wastewaters, accidental inputs and coastal human activities [8,11]. In terrestrial ecosystems, the ingestion of plastics by livestock may lead to nutritional deficiencies in the animals. Plastic pollution has attracted attention as a growing threat to marine ecosystems. Conservative estimates of overall financial damage of plastics to marine ecosystems stood at $13 billion per year in 2014 . Marine environments consists of about 10% of the total plastics produced . It is estimated that of all the waste present in the aquatic environment, about 60%-80% is plastic . As plastic is a synthetic product, its sources are mostly inland . The quantity of plastic waste available to enter the marine environment from land is alarming. It is estimated to increase manifold with insufficient waste management infrastructure improvements . A study conducted by United Nations Joint Group of Experts on the Scientific Aspects of Marine Pollution (GESAMP) concluded that 80% of the waste in the marine environment originates from land, while only 20% was a result of activities at sea .
The larger plastic debris, known as “macroplastics” tend to accumulate in specific areas of the ocean as a result of convergence of surface currents . As the plastic waste enters into the marine environment, various factors begin to have a degrading effect on the plastic material. Long-chain plastic macromolecules are degraded into shorter chains of lower molecular weight. Plastic degradation can occur under the influence of various environmental factors such as heat, light, mechanical force, water and chemicals [1,12]. The degradation can be classified as thermal, photooxidative, ozone-induced, catalytic or mechanochemical degradation or biodegradation . Prolonged exposure to UV radiation from sunlight can cause oxidation of the polymer matrix, resulting in bond cleavage . Such degradation may result in leaching out of additives, which are originally meant to enhance durability and corrosion resistance of plastics . Because of the loss of structural integrity, these plastics become susceptible to fragmentation resulting from abrasion, turbulence and wave action [19,23]. Consequently, the macroplastics degrade over spatial and temporal variations into smaller pieces. As the production of plastic has increased exponentially over the last five decades, the smaller pieces have progressively become more widespread in the marine environment. These small plastic particles can be classified based on their size as “microplastics” or “nanoplastics” .
Microplastics were first introduced to the world in 1972 when small-sized plastic particles were reported to be floating on the surface of the Sargasso Sea . Microplastic was defined by the Steering Committee of National Oceanic and Atmospheric Administration (NOAA) Marine Debris Program as being a plastic less than 5 mm in size along its longest dimension . Microplastic generally refers to any piece of plastic smaller than 5 mm to 1 pm in size along its longest dimension. A piece of plastic less than 1 pm in size is referred to as a nanoplastic. Due to the extremely small size of nanoplastics and the associated difficulties in their detection and recovery, most studies on the marine ecosystems tend to overlook nanoplastics and instead focus on microplastics. However, the presence of nanoplastics in the marine environment is likely to become increasingly significant in the years to come, and researchers have already begun to speculate on the effect of nanoplastics on the marine food web .