Initial Inventory of Plastics Imports in Nigeria as a Basis for More Sustainable Management Policies

Background. Plastic is a waste stream with recycling and recovery potential. However, the recycling rates for plastic in African countries are low. Furthermore, use and production of virgin plastics are increasing. Therefore, a high proportion of plastic waste is being disposed of in landfills and dumpsites. Plastic serves as fuel for open burning at landfills/dumpsites with associated releases and constitutes a large fraction of marine litter, making it a major and growing global pollution concern. Objectives. This study aims to develop an initial inventory of plastics in Nigeria towards the development of an effective plastics management frame. Methods. A search was conducted of the recent literature and the United Nations (UN) Comtrade database using harmonized system (HS) codes for import data of various polymer categories and major product categories containing plastic. Algebraic expressions were developed for calculation of the share of plastic in these products. Results. Approximately 14,200,000 tons of plastics in primary form were imported into Nigeria between 1996–2014. Approximately 3,420,000 tons total plastic were imported in the form of products and approximately 5,545,700 tons were imported as product components. Approximately 194,000 tons of plastic toys were imported over a six-year period. Discussion. The total amount of plastics imported in primary form and as products equals 17,620,000 tons. The total volume of imported plastic, newly produced plastic and plastic components going into the technosphere was 23,400,000 tons. The huge amount of plastic and other polymers entering the technosphere in Nigeria has important implications for marine litter, pollution, waste management and resource recovery. Conclusions. A huge volume of plastics has entered the Nigerian technosphere, with less than 12% of the resulting waste entering the recycling stream. There is a need for sustainable management of this crucial waste and resource category. Potential mitigating strategies include waste plastic reuse, recycling, waste conversion to energy, and appropriate plastic control policy frameworks. Competing Interests. The authors declare no competing financial interests.


Introduction
Plastics are materials or products made from a wide range of polymers of high molecular mass. They have broad applications in time and space due to their durability, ease of production, low cost and relatively light weight. Recent decades have witnessed a tremendous increase in plastic used in a wide range of products. Global production of this commodity increased from 1.5 million tons (Mt) per year in 1950 to 245 Mt in 2008, and it has been projected that global plastic production could triple by 2050. 1 Its use has increased twentyfold in the past half-century and is expected to double again in the next 20 years. 2 Plastic is increasingly replacing metals, glass, ceramics and wood in many products. Plastic packaging materials are now employed Background. Plastic is a waste stream with recycling and recovery potential. However, the recycling rates for plastic in African countries are low. Furthermore, use and production of virgin plastics are increasing. Therefore, a high proportion of plastic waste is being disposed of in landfills and dumpsites. Plastic serves as fuel for open burning at landfills/dumpsites with associated releases and constitutes a large fraction of marine litter, making it a major and growing global pollution concern.
in the food, beverage and other fastmoving consumer goods industries. 3 However at their end-of-life, plastics present solid waste management challenges. The challenge of plastic waste management, particularly recycling, is a global issue, especially in African countries where robust waste management systems are lacking.
Plastic is a waste stream with recycling and recovery potential. 4 However, the rate of recycling is not keeping up with the rate at which virgin plastics are being produced and a higher proportion of plastics is being disposed of in landfills and dumpsites than ever before. 5 Very few polymers are recycled on Research a large scale. 6 The recycling and recovery rates for plastic in African countries are low. Furthermore, waste plastics may contain hazardous substances, thereby limiting the scope of recycling. 7, 8 Emission of volatile organic compounds during recycling may pose acute and chronic health risks in recycling workshops. 9 A broad range of plastics contain endocrine-disrupting chemicals such as phthalates or brominated or chlorinated flame retardants. 10-12 Such contaminants are not commonly removed in recycling of household plastics. 13 Marine litter has become a global and regional issue affecting the quality of marine and coastal environments. 14 It constitutes a major threat to marine animals. 15, 16 The volume of marine litter is continually growing. Recent studies have shown that litter quantities on some beaches will exceed present levels by 250 times in 10 years. 17 The majority of litter is from land-based sources. Plastic constitutes a larger fraction of marine litter and has become a major and growing global pollution concern. 18 Globally, 6.1 billion tons of plastics have been produced, and it has been estimated that about 10% of this will be deposited long-term in the world's oceans. 19 It is estimated that 275 Mt of plastic waste was generated in 192 coastal countries in 2010, with 4.8 to 12.7 Mt entering the ocean, of which 0.25 to 1.00 Mt from Nigeria was available to enter the ocean in 2010. 20 This deposition becomes a sink for microplastics in the Arctic sea ice, and can persist in the marine environment for hundreds of years. 1,21 Marine litter is increasing on the deep Arctic seafloor and spreading to the north. 22,23 The regional contribution to the increasing volumes of marine litter along with pollution on land and open burning is an issue that needs to be urgently addressed, particularly in developing countries.
The lack of appropriate solid waste management is a major problem in Africa and other developing countries and a major reason for plastic pollution. 24,25 The region is faced with challenges due to inadequate technological capability and ineffective waste collection systems. There is no source separation of solid waste in Nigeria and therefore a larger fraction of waste plastic and other polymers end up at dumpsites together with other disposed wastes. A preferred management option for plastic is recycling, which is being practiced to an extent in this region. In addition to a limited technical recycling capacity, there is a risk of contamination of recycled plastic by hazardous substances. 8, 26 Polymers that do not get into the recycling stream are disposed of through open burning and landfill fires with associated pollution releases. Another share of plastic is dumped in streams and rivers. 25 Recent studies have shown that rivers are a source of marine litter, and Nigeria ranks 6th in global plastic marine litter release. 27 Thus, there is an urgent need for more effective management of waste plastics in developing countries such as Nigeria. There is a need for adequate information on plastic/polymer quantities and categories of plastics in Nigeria in order to improve plastic management and to set appropriate and effective policies and incentives.
Although there is growing concern over plastics and related pollution, robust national and regional information is lacking in Africa. A detailed assessment of material/ pollutant imports into this region is useful as a baseline for future efforts to reduce pollution levels. Furthermore, the background metric is crucial to accurately measure increases in pollution and as a tool to measure subsequent efforts to reduce pollution levels. Therefore, the present study identifies and synthesizes dispersed data on the import and production of plastic and presents the first national analysis of this data. In addition to compiling information on the import and production of plastic in Nigeria, data is presented concerning plastic imported in products such as cars, washing machines, air conditioning machines, refrigerators, consumer electronics and IT and telecommunication equipment, and toys. In addition, data gaps are identified in our understanding of the overall plastic stock in Nigeria in order to facilitate policy development.

Methods
The present study method involved a search through the United Nations (UN) Comtrade database using harmonized system (HS) codes for import data of various polymer categories and major product categories containing plastic (see Supplemental Material 1). 28,29 The recent literature was also searched to identify products which contain significant amounts of plastic (e.g. plastic in electrical and electronic equipment (EEE) and waste electrical

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and electronic equipment (WEEE), the transport sector and other applications). The share of plastic in these products was calculated. Data gaps and inconsistencies were identified and an approach for data improvement is described.
For a reasonable estimation of imported plastics, the assessment covered plastics imported as products and as components of products. As there are numerous products containing polymers imported into Nigeria, the estimation process is complex. In order to simplify our approach, mathematical models or algebraic expressions were developed and applied where appropriate and are shown in Table 1. The main products considered to contain considerable amounts of polymers were refrigerators, washing machines, air conditioning units, consumer electronics, IT and telecommunications equipment, and toys. The assessment covered the period from 1996-2014.  Table 3. Table 4 presents information on the various categories of plastics imported as products into Nigeria. M i is the total plastic (not as product components) imported; M p1 is the total amount of plastic imported in primary form; M p2 is the total amount of plastic imported as products.

Plastic and other polymers imported in products
M ic is the amount of plastic imported as product components; M p is the amount of a particular product imported; f p is the fraction of plastic in a particular product. T pv is the total polymers in motor vehicles; M pv is the total amount of plastic; M pur is the total amount of polyurethane foam. The total amount of polymers imported as components of motor vehicles in Nigeria is shown in Table 6. The total amount of polymers (plastic + polyurethane foam) is estimated to be 2,932,128 tons, including 2,531,128 tons plastic and 401,000 tons of polyurethane foam.

Polymer content of refrigerators
The amount of plastic contribution from various sources is summarised in Table 10. The total amount of plastic and polymers imported in primary form was 14,200,000 tons, the total amount of plastic and other polymers in major imported products was 3,420,000 tons, and the total amount of plastics imported in primary form and as products was 17,620,000 tons. Therefore, the total volume of imported plastic, newly produced plastic and plastic product components going into the technosphere from 1996-2014 was estimated to be 23,400,000 tons.

Discussion
The present assessment identified the contribution of imported plastics across a wide range of products, including plastics imported as products and as components of products to estimate the amount of plastic entering the technosphere in Nigeria during the study period.

Plastics imported as products
The total amount of plastics imported as products between 1996-2014 was approximately 3,420,000 tons.
This represents about one-quarter of plastics imported in primary form. This shows that plastic products are generally produced from imported primary plastics in Nigeria rather than being imported. The imported products include rods, tubes, pipes and hoses, floor coverings (rolls and tiles), wall coverings, ceiling covering, plates, sheets, builders' wares, reservoirs, tanks, articles of apparel and clothing accessories (including gloves, mittens and mitts), fittings for furniture, and ornamental articles.
These products are mainly comprised of construction and household materials, which are now old enough for replacement (import reporting started in 1996, approximately 20 years ago). While reservoirs and tanks at their end-of-life form a considerable fraction of the recycling stream, other products in this category usually end up in dumpsites. When buildings are demolished, concrete, wood and metals are targeted for reuse/recycling, while plastic materials are usually disposed of in dumpsites.

Plastic consumer product components
There are fractions of plastic which are components of other products. The amount of this plastic constituting product components is significant in the overall volume present in Nigeria. Such products include electrical and electronic equipment like refrigerators, air conditioners, household or laundry washing machines, consumer electronics and IT and telecommunications equipment. In addition, motor vehicles contain a considerable and increasing share of plastic and other polymers. At their end-of-life, these also represent a large waste stream. Plastic from e-waste and light fraction of car shredder residues are a particular challenge in waste management and recycling in

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Nigeria and in industrial countries as well. 8,47,[48][49][50] Toys are largely made of plastics and are an important contributor to total household plastics and of concern with respect to human exposures, in particular for vulnerable infants and children. These major consumer products were therefore also assessed for their contribution to the total plastic stock in Nigeria.

Refrigerators
The import of refrigerators (new and second-hand) into Nigeria is continually increasing. A total of 456,000 tons of refrigerators were imported during the study period, containing 145,920 tons of plastic and polyurethane foam. The amount present in Nigeria might be higher than what has been reported. There are local assemblers/manufacturers in the Nigerian EEE sector who often import parts for assembly into Nigeria. According to the Nigeria e-waste country assessment, the volume of assembled/manufactured refrigerators in the country between 2001 and 2005 alone was 124,781 tons. 50 Therefore, the amount of polymers present in refrigerators in Nigeria is considerable larger than this estimate. The prevalence of refrigerators in urban households is 100% (with average number of 1.27 per household), and approximately 20% in rural areas (with average number of 0.23 per household). 50

Consumer electronics and IT and telecommunications equipment
Major plastic volumes in EEE/WEEE stem from consumer electronics and IT and telecommunications equipment. The IT and telecommunications equipment (European Union WEEE category 3) include fax machines, landline and mobile phones, laptops, personal computers, monitors (cathode ray tubes and flat panels), modems, printers, scanners, copy machines, uninterruptible power supplies (an electrical apparatus that provides emergency power to a load when the input power source or mains power fails) and inverters.

Motor vehicles
A total of 224,165 tons of polymers (plastic + polyurethane foam) are estimated to have been imported into Nigeria from 1980-2010. Vehicles are another major source of plastics and polymer imports into Nigeria. Plastic car body parts include spoilers and bumpers, instrument panels and headlights, side trim and interior trim, seats and airbags, carpets, tires, seals and gaskets, fan belts, gearbox mountings, engine covers, etc. 52 The main polymers used in their manufacture include polypropylene, polyurethanes, nylon, polyvinyl chloride, ABS, polyethylenes, polycarbonate, and polyvinyl butyral. 53 The average percentage of plastic in cars and buses is 9.1% and 8.4% in trucks, respectively, as used for estimations in this study. 53,40 The plastic share in vehicles is increasing. Recent models of cars may have up to 15% plastic share of their total weight. 52 These plastic/polymers end up in the light shredder fraction in the management of end-of-life vehicles and are a waste management challenge. 13 Toys Between 2009  Globally, as of 2015, the amount of plastic waste generated was 6300 Mt, and of this, 9% was recycled, 12% incinerated, and 79% accumulated in landfills. 62 In the European Union, around 25 Mt of plastic waste was generated in 2008. 1 However, industrialized countries with separation schemes and in place legislation have high recycling and recovery rates. In these countries, plastics may be recycled or shipped to China or India for recycling. In India, 47% of the total plastic waste generated is recycled. 42

Study data
The data compiled for the present study was evaluated for reliability, gaps and inconsistency.

Gaps and inconsistency of import data in UN Comtrade
Data for the years 2004 and 2005 were missing for all imported plastics in primary form and as products. In other cases, data for one or more years were missing for a category of products. This does not mean that plastics were not imported during this period (zero was recorded where there was no import), but that the database did not receive information for the respective period/year and HS category. Due to this missing data, the actual amount of plastic imported is somewhat higher than reported in this paper.
In addition, the data revealed some particularly high import rates in 2009 and 2010. These years were unique in Nigeria's economy, including for import of goods. Generally, import of all goods in Nigeria reached an all-time peak in 2010, and import partners included China, Belgium, Netherlands and the United States of America. 64 Import of finished goods was also highest in 2010. 65 Import of construction materials was generally high in Nigeria in 2010, and imported polymer materials for construction include roofing sheets, PVC tanks, PVC tiles, and PVC plumbing materials. 66 In addition, there was a peak in the import of used electrical electronic equipment around 2010 in Nigeria after China strongly reduced importation of WEEE around 2006. 8 Other factors responsible for high import rates may include an increase in population from 120 million in 2000 to 160 million in 2010. Apart from 2010, there were some high import rates within specific categories for various years. It may be that relevant industries or manufacturers had special orders resulting in higher volumes over those periods. However, it was not possible to trace individual data and industries for confirmation.
The import data for a country are usually recorded with relative accuracy as imports generate tariff revenues. Therefore, the higher/lower data points were considered to be accurate in the Comtrade database.

Plastic fractions not fully addressed in this study
Only major consumer products containing plastic were included in the current analysis. In terms of EEE/WEEE, only category 3 (IT and telecommunications equipment), category 4 (consumer equipment), category 1 (white goods) and air conditioners were considered. Plastic in small household appliances as well as packaging materials of imported products such as polystyrene packaging or polymer wrapping were not included due to the lack of data. While this approach underestimates the total volume of plastic imported via EEE, the major plastic imports were covered in the present study.

Selected time frame and material flow analysis
The present study covered the period from 1996-2014 for the compilation of plastic import data. While plastics were imported before 1996, this time period is most relevant due to the increasing use of plastic over the last 20 years. The plastic imported over the last two decades has entered the technosphere, while plastic imported before 1996 has generally been disposed of in landfills and dumpsites over the last two decades. A considerable share of the plastics imported since 1996 have reached end of life (EoL) and been disposed of or subject to open burning, including plastic used for disposable goods like packaging or plastic bags. For other plastics such as water pipes or plastics used for window frames or other construction, the largest share is still in use. For plastics in consumer goods such as electronics or vehicles, their status depends on particular product life spans. For an assessment of the stocks and flows of plastic, a material flow analysis for individual products is needed, which is beyond the scope of the present study which compiled primary data on plastic imports to Nigeria. Preliminary material flows have been established by our previous research on brominated POPs in plastic from selected WEEE fractions and in polyurethane foam in vehicles produced between 1970-2004, establishing initial material flow data for Nigerian plastic fractions. 8, 25 Further study is needed to address the previously mentioned data gaps and to improve available data.

Conclusions
More than 23,400,000 tons of plastics entered the Nigerian technosphere between 1996-2014, with less than 12% of the resulting waste in the recycling stream. Considering the risks this volume presents to global and local environments and human health, there is the need for sustainable management of this important waste and resource category. 67 Potential mitigating strategies may include waste plastic reuse, recycling, waste conversion to energy, and appropriate plastic control policy frameworks. Policies should address the waste hierarchy with an emphasis on waste reduction and recycling. Energy recovery using cement kilns is a promising mitigation solution, as cement kilns in Nigeria do not at present use any secondary fuel.
The present study demonstrated a novel application of international trade data to the estimation of plastic volume flow and associated pollution potential in a developing country. The connection of international trade and inventory data and related waste/ pollution potential is a powerful tool that can be used to develop countermeasures and improve prevention and management programs. Furthermore, as there was no previously established methodology for this assessment in Nigeria or the region of Africa as a whole, the approach in this study may serve as a model for similar studies in other developing countries. The data obtained in this study can serve as basis for policies to improve plastic waste management in Nigeria and for future studies refining the dataset and more detailed material and substance flow analyses.