Quantification of PAHs, PCBs and Pesticides adsorbed by plastic waste in the Togolese marine environment

doi:10.21203/rs.3.rs-3587256/v1

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Quantification of PAHs, PCBs and Pesticides adsorbed by plastic waste in the Togolese marine environment

https://doi.org/10.21203/rs.3.rs-3587256/v1

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The study aims to determine the different pollutants adsorbed by plastic waste along the Togolese coast. To this end, nine samples were taken from three different sites and analysed by GC-MS and LC-MS. Apart from pesticides, which were found in only one sample, PAHs and PCBs were adsorbed by all nine samples collected. Thus, the total concentrations of PAHs and PCBs at the different sites give respectively in ng/g; at Aneho, 677.16 and 26.95 on the LDPE debris, those of PP are 195.92 and 8.85; 136.34 and 4.04 on the PET sample. At Kodjoviakope, 596.5 and 14.6 on the LDPE sample; those of PP are 196.46 and 11.37; 105.15 and 1.6 on the PET sample. In the Fishing Port, 1182.56 and 9.87 on the LDPE sample, PP 336.57 and 13.04; 274.06 and 2.74 on the PET sample. There is a need to take measures to eradicate their presence at sea.

fragmentation

marine plastic debris

adsorption

PAH

PCB

pesticides

The world's population continues to grow; estimated at seven billion yesterday, it is now around eight billion (UN, 2023). This exponential population growth leads to a huge global consumption and in particular to a massive recourse to plastic materials, whose duration of use is negligible compared to the time required for their degradation. Being a macromolecule that is obtained by adding several identical molecules (monomers) and that after heating can be shaped, flexible or rigid (Carrega et al., 2012), plastic can be used in many fields. This versatility of plastics combined with the population explosion has increased its use. However, the mismanagement and lack of information about the harmful effects of plastics has led to our planet becoming a plastic planet. Thus, the marine world is full of plastic waste as everything converges on it through deflation and run-off. Plastics account for 50–80% of all waste and sometimes even 100% in the case of floating debris (Galgani, 2020). The accumulation of plastic waste in aquatic environments is a crucial environmental problem because of its impact on ecosystems. Firstly, macroplastics floating on the sea sometimes cause the death of large marine organisms by accidental capture or intestinal obstruction (Lavers et al., 2014 ; Li et al., 2016 ). Secondly, as these macroplastics break down into smaller particles, these particles mix with food sources, impacting smaller marine organisms such as mussels, copepods, fish and bivalves (Bowne et al., 2008 ; Cole et al., 2013 ; Rochman et al., 2015).

Also, the fragmentation of plastic waste into smaller and smaller particles gives them a high surface to volume ratio. This property gives them the ability to adsorb metals and persistent organic pollutants (POPs) from the marine environment (Lee et al., 2013 ; Boucher et al., 2016 ; Fred–Ahmadu et al., 2022). As plastic particles age, they develop new anionic active sites, which increases their exchange surface area and adsorption capacity (Holmes et al., 2014). This puts the health of marine fauna at risk as the more the plastic crumbles, the more it adsorbs pollutants and mixes with food sources ingested by marine fauna. Indeed, several studies have shown that these POPs are toxic and endocrine disruptors (Hirai et al., 2011 and Ogata et al., 2009). Other recent studies on microplastics in the Gulf of Guinea region, specifically in Nigeria, have demonstrated the existence of Polycyclic Aromatic Hydrocarbons (PAHs), Polychlorobiphenyl (PCBs) and pesticides with concentrations of 0.00–0.32 mg/kg, 0.00–0.53 mg/kg and 0.04–2.02 mg/kg respectively (Fred-Ahmadu, 2022). As the Togolese coast is located on the Gulf of Guinea, it will not be immune to the problem created by plastic waste. Through run-off, deflation and marine currents, the Togolese coast receives a great deal of plastic waste, which gradually degrades, creating a favourable environment for the adsorption of POPs. With this in mind, this study was carried out to identify some of the pollutants adsorbed by plastic waste along the Togolese coast. The study was carried out on three types of plastic ; Low Density Polyethylene (LDPE), Polyethylene Terephthalate (PET) and PolyPropylene (PP), since these are the ones most frequently found when characterising solid marine waste. The results obtained will enable us to consider what action needs to be taken to inhibit this phenomenon.

2.1. Presentation of the study site

The study is conducted in the Maritime region, a region located in the south of the country, bordering the Atlantic Ocean, to the north by the Plateau region, to the east by Benin and to the west by Ghana. It extends between 6°00' and 6°50' North latitude and 0°25' and 2°00' East longitude. It covers an area of 6,395 km², i.e. 11.30% of the national territory. Like the other coastal areas of the countries of the West African region, the population of the Maritime region is characterised by strong demographic growth (3.16%) in 2010. Indeed, the region concentrates 42% of the national population, which is about half of the Togolese population (DSCN, 2012).

2.2. Collection of samples

This work was carried out at three sites: Aneho, Kodjoviakope and Fishing port. Three types of plastic waste from fishing nets were collected at each site. These were LDPE (Low Density Polyethylene), PP (Polypropylene) and PET (Polyethylene Terephthalate). It should be noted that the plastic waste collected at these sites is identical or similar in nature. A total of nine samples were collected in August 2022, three from each site. Aluminium foil was used to cover the samples to prevent contamination. The samples were then stored in a freezer at -5°C. Pictures 1 and 2 show the type of plastic and the number of samples collected, respectively.

2.3. Experimental procedure

Overview

The reference method used was adapting the method of Núñez et al. (2022). The analysis was performed using the Agilent 6420 Triple Quad LC/MS and Agilent 7890B GC with 7000C GC/MS.

2.3.1. Solvents, Reagents and Chemicals

All reagents and solvents were HPLC or analytical grade. Dichloromethane was from VWR Chemicals (VWR International SAS, France), Acetone was from Carlo ERBA Reagents (France) and Hexane from Chem-Lab NV (Belgium). Bond Elut C18 Solid Phase Extraction (SPE) Cartridge was from Agilent Technologies, Inc. (California, United States). Pesticides, PAH and PCBs standards were from Dr. Ehrenstorfer GmbH (Augsburg, Germany). The standards for PCBs, PAHs and pesticides are listed in Table 1

Table 1

Analytical reference substances for PCBs, PAHs and pesticides
PCBs	PAHs	Pesticides
PCB 18	Naphthalene	Acephate
PCB 28	Acenaphthene	Aclonifen
PCB 44	Acenaphthylene	Allethrin
PCB 52	Fluorene	Ametryn
PCB 101	Phenanthrene	Atrazine
PCB 118	Anthracene	Azinphos-Ethyl
PCB 138	Fluoranthene	Bensulfuron-methyl
PCB 149	Pyrene	Boscalid
PCB 153	Benz[a]anthracene	Bromacil
PCB 170	Chrysene	Chlorfenvinphos
PCB 180	Benzo[b]fluoranthene	Chlorpyrifos
PCB 194	Benzo[k]fluoranthene	Difenconazole
PCB 209	Benzo[e]pyrene	Dimethoate
	Benzo[a]pyrene	Dimethomorph
	Perylene	Emamectin benzoate
	Benzo[g,h,i]perylene	Fluazinam
	Dibenz[a,h]anthracene	Fluopyram
	Indeno[1,2,3-cd]pyrene	Imidacloprid
		Indoxacarb
		Kresoxim methyl
		Metalaxyl
		Methamidophos
		Metolachlor
		Monocrotophos
		Nicosulfuron
		Pirimifos-methyl
		Prochloraz
		Promecarb
		Propaquizafop
		Pyrimethanil
		Pyriproxyfen
		Spiroxamine
		Sulfoxaflor
		Terbuconazole
		Terbufenozide
		Terbutryn
		Thiamethoxam
		Topramezone
		Triadimefon
		Triadimenol
		Trifloxystrobin

2.3.2. Extraction

To extract an organic pollutant (PAHs, PCBs and pesticides), 1 g of plastic sample (± 0.05 g) is shredded and placed in a 50 mL bottle. A mixture of 30 mL acetone and dichloromethane (1:1 by volume) is then added. The flasks were then closed and shaken for 24 hours at 25°C. Once extraction was complete, the samples were filtered through glass wool and 2 g of sodium sulphate. They were then concentrated at a temperature below 40°C on a rotary evaporator to a final volume of approximately 1 mL. A new 1 g sample was reused for analysis to estimate the standard deviation. All samples were cleaned using C18 solid phase extraction (SPE) cartridges to remove impurities and dissolved plastic during extraction. Extracts were transferred to SPE C18 cartridges preconditioned with 5 mL dichloromethane and 5 mL hexane. A total of 10 mL of hexane was used to elute the samples. After cleaning, all the samples were reconcentrated at a temperature below 40ºC on a rotary evaporator until they were dry. As a first step, the residue obtained was again dissolved in 1 mL ethyl acetate. The extract was transferred to a 2 mL standard opening vial for GC-MS quantification of PAHs and PCBs. This residue was then dissolved in 1 mL of acetonitrile for LC-MS quantification of pesticide residues.

2.3.3. Preparation of standard/stock solutions

Analytical standard solutions were prepared for fortification and calibration. Pesticides were solid and prepared in acetonitrile. Primary stock solutions of pesticides were prepared from the pure analytical reference substances (ARS) listed in Table 1. PCB and PAH standard solutions were dissolved and diluted to concentrations of 1 µg/mL. Working solutions were diluted from the stock solutions. The fortification standards were used to fortify the controls. Additional standards were prepared and used as external calibration solutions at 10 µg/mL, 20 µg/mL, 50 µg/mL, 100 µg/mL and 200 µg/mL for quantification. Ethyl acetate was used to prepare standards/stocks for PCBs and PAHs. Table 1 illustrates the PCB and PAH standards used.

2.3.4. Instrument Conditions

Table 2

Summary of chromatographic conditions for determination of pesticides on LC-MS
Apparatus:
Instrument	Description
Liquid Chromatograph/Mass Spectrometry	Agilent Technologies-Infinity 1290 LC System with a 4226A Autosampler, 4204A Quaternary Pump, G1316C Temperature Control Compartment. Agilent 6420 Triple Quadrupole MS System
Analytical column	Agilent-Zorbax Eclipse Plus C-18 Rapid Resolution HD Column with specifications 2.1 x 50mm 1.8-Micron
Injection Volume	6 µl
LOQ	10 µg/kg
LOD	5 µg/kg
Solvent Program	Time	Solvent A – 0.1% formic acid in water	Solvent B – 0.1% formic acid in acetonitrile
	1 min	95	5
	2 min	85	15
	2.5 min	70	30
	6 min	55	45
	12 min	20	80
	14 min	5	95
	16 min	5	95
	18 min	95	5
Mass Spectrometer:
Item	Conditions
Source Gas Temperature	300°C
Gas Flow	13 l/min
Nebulizer	30psi
Capillary	Positive 4000V
Scan Type	Dynamic MRM
Delta EMV	350V

Table 3

Summary of chromatographic conditions for PAH and PCB
Apparatus:
Instrument	Description
Gas Chromatograph	Agilent 7890 B GC with a Agilent Technologies GC sampler 80
Analytical column	30m + 10m EZ Guard x 0.25mm internal diameter fused silica capillary coated with VF-5ms (0.25µm film) from Agilent or equivalent.
Liner	Agilent 5190 − 3167:900UL Single Tapered
Mass Spectrometer	Agilent 7000C Triple Quadrupole
Temperatures:
Item	Conditions
Injector	Splitless mode, temperature 280°C
Injection Volume	1 µl
LOQ	5 µg/kg
LOD	1 µg/kg
MSD Transfer Line	325°C
Gases:
Gas	Flow rate
Helium (carrier)	2.25 ml/min constant flow
Collision gas (Nitrogen)	1.5 ml/min constant flow
Septum purge	30mL/min at 0.75min
Pressure	27.5psi
Mass Spectrometry
Source Temperature	300°C
Scan Mode	MRM
Ionization mode	EI

2.3.5. Quality Control

Solvent Blank: A solvent blank (Acetonitrile), devoid of any plastic matrix, was prepared using the same solvents employed in the extraction and analysis processes. This blank ensured that the solvents did not introduce any interference or contamination during the analysis.

Matrix Blank: A matrix blank was obtained from a new plastic bag made from LDPE plastic No. 4. This matrix blank was subjected to the same sample preparation steps as the actual plastic samples, excluding the addition of PAH, PCBs, and pesticide standards. It served as a control to evaluate potential contamination or interference from the plastic matrix.

Spiking of Matrix Blank: The matrix blank was spiked with pure PAH, PCBs, and pesticide standard solutions to assess the accuracy of the analysis. A known concentration of each standard was added to the matrix blank to simulate the presence of these compounds in the plastic sample. The weight of the spiked sample taken was 1g, and the standard concentration used was 1µg/ml, with a standard volume of 0.1 ml. The expected recovery level was set at 100 µg/kg.

Spike volumes of pure standards was calculated as;

Spiked Volume (mL) = \(\frac{\text{S}\text{a}\text{m}\text{p}\text{l}\text{e} \text{w}\text{e}\text{i}\text{g}\text{h}\text{t} \left(\text{g}\right) X \text{S}\text{p}\text{i}\text{k}\text{e}\text{d} \text{l}\text{e}\text{v}\text{e}\text{l} (\text{u}\text{g}/\text{m}\text{l})}{Standard Concentration \left(\frac{ug}{ml}\right)}\) Eq. 1

Spike volume was distributed evenly on free sample (blank) and the spiked sample analyzed for percentage recovery which was calculated as;

%Recovery =\(\frac{\text{C}\text{o}\text{n}\text{c}\text{e}\text{n}\text{t}\text{r}\text{a}\text{t}\text{i}\text{o}\text{n} \text{i}\text{n} \text{s}\text{p}\text{i}\text{k}\text{e}-Concentration measured in the blank}{Spiked Concentration} X 100\) Eq. 2

The samples analysed ranged from 60 to 110% recovery. The limit of detection (LOD) values were 1 µg/kg for PCBs and PAHs and 5 µg/kg for pesticides. The limit of quantification (LOQ) was 5 µg/kg for PCBs and PAHs and 10 µg/kg for pesticides.

Calibration Standards: Calibration concentrations of PAH, PCBs, and pesticides (10 ppb, 20 ppb, 50 ppb, 100 ppb, and 200 ppb) were prepared using appropriate stock solutions. These calibration standards were run prior to the analysis of the plastic samples to establish a calibration curve. The calibration curve enabled the quantification of the target compounds in the plastic samples.Verification standard of the mixed pesticide residues, PAH and PCBs (100µg/ml) was run before, in between and after the analytical extracts to guarantee precision and accuracy of the analytical results.

3.1. Determination of PAHs

3.1.1. Concentration of PAHs in ng per gram in LDPE plastic debris

Figure 2 presents the results of the analysis of the three LDPE samples collected at the three sites (Aneho, Kodjoviakope and Fishing Port). Fifteen (15) PAHs were detected in all three LDPE samples submitted for analysis. It turns out that Acenaphtene, Acenaphtylene and Dibenz⌈a,h⌉anthracene were not detected on these analysed samples. The highest observed concentration of PAH is Indeno[1,2,3-cd] pyrene with a value of 176.75 ng/g; this concentration is detected at the Fishing Port Port. The smallest is Fluorene ; at all three sites Fluorene has the lowest concentrations. In sum, of the 15 PAHs detected, the dominant ones are successively Indeno[1,2,3-cd]pyrene, naphthalene, Benzo[e]pyrene, pyrene, Benzo[a]pyrene.

3.1.2. Concentration of PAHs in ng per gram in PP plastic debris

Figure 3 presents the results of the analysis of the three PP samples collected from the three sites (Aneho, Kodjoviakope and Fishing Port). Nevertheless, several PAHs were detected in each sample from the three sites. For example, in Aneho, 11 PAHs were detected, 11 PAHs were also detected in the Fishing Port and 8 PAHs in Kodjoviakope. Acenaphtene; Dibenz⌈a,h⌉anthracene, Benzo[e]pyrene, Benzo[a]pyrene, Perylene and Indeno[1,2,3-cd]pyrene were not detected on these analysed samples. The highest observed concentration of PAHs at all sites is Naphthalene. Its respective values in ng/g are 114.6; 125.84; 149.05 in Aneho, Kodjoviakope and Fishing Port. The lowest value of PAH concentrations is Benzo[g,h,i]perylene detected at the Fishing Port site with a concentration of 3.56 ng/g.

3.1.3. Concentration of PAHs in ng per gram in PET plastic debris

The concentrations of PAHs detected on PET plastic debris at the three sites are presented in Fig. 4. Of the 18 PAHs listed only 9 were detected on the samples submitted for analysis. Acenaphtene, Benzo[b]fluoranthene, Benzo[k]fluoranthene, Benzo[g,h,i]perylene, Dibenz⌈a,h⌉anthracene, Benzo[e]pyrene, Benzo[a]pyrene, Perylene and Indeno[1,2,3-cd]pyrene were not detected on these analysed samples. Naphthalene has the highest concentration with 160.43 ng/g at the Fishing port, 73.18 ng/g at Aneho and 63.9 ng/g at Kodjoviakope respectively. The lowest value of PAH concentrations is Chrysene detected at the sites of Fishing port and Aneho with respective concentrations of 4.9 ng/g and 3.17 ng/g.

3.1.4. Sum of PAH concentrations

Figure 5 compares the amount of PAHs in the three types of plastic debris and at the three sites. At the Aneho site, the total sum of PAH concentrations on LDPE is much higher (677.16 ng/g) than the sum of PAH concentrations on PP (195.92 ng/g) and the sum of PAH concentrations on PET (136.34 ng/g). Also at the Kodjoviakope site, the total sum of PAH concentrations on LDPE is much higher (596.5 ng/g) than the sum of PAH concentrations on PP (196.46 ng/g) and the sum of PAH concentrations on PET (105.15 ng/g). The sum total of PAH concentrations on LDPE still ranks first at the Fishing Port site with a value of 1182.6 ng/g followed by the sum total of PAH concentrations on PP (336.57 ng/g) and 274.06 ng/g on PET. Also, of the three sites, it is at the Fishing Port site that there is more PAH absorption on LDPE, PP and PET. Taking into account the sum of PAH concentrations on all the plastic debris, the Fishing Port represents the site where there is more PAH absorption, followed by Aneho and Kodjoviakope.

3.2. Determination of PCBs

3.2.1. Concentration of PCBs in ng per gram in LDPE plastic debris

The results of the analysis of the three LDPE samples collected at the three sites (Aneho, Kodjoviakope and Fishing Port) are presented in Fig. 6. 100% of the samples showed the presence of several PCBs. Of the 13 PCBs identified, only two were not detected after analysis. These are PCB 118 and PCB 209, so 11 of the 13 PCBs were detected with a concentration of between 0.04 and 6.92 ng/g in the three LDPE samples submitted for analysis. PCB 138 is the most abundant with 5.26 ng/g in Aneho, 5.95 ng/g in Kodjoviakope and 4.03 ng/g in the Fishing port. The highest observed concentration of PCBs is PCB 149 with 6.92ng/g; this concentration is detected at the Aneho site. The lowest concentration is PCB 101 with a value of 0.04 ng/g and is detected at the Kodjoviakope site. The main PCBs found are PCB 138, PCB 149 and PCB 153.

3.2.2. Concentration of PCBs in ng per gram in PP plastic debris

According to Fig. 7, seven (07) PCBs were detected in the three PP samples submitted for analysis. The analysis reveals that PCB 118, PCB 153, PCB 170, PCB 180, PCB 194 and PCB 209 were not detected in these samples. PCB 138 is the most abundant with 3.23 ng/g in Aneho, 4.46 ng/g in Kodjoviakope and 4.49 ng/g in the fishing port. Its concentration is also the highest with a value of 4.49 ng/g detected at the fishing port. The smallest concentration is PCB 101 with a value of 0.04 ng/g and it was detected at the Kodjoviakope site. The main PCBs found are PCB 138, PCB 149, PCB 18 and PCB 28.

3.2.3. Concentration of PCBs in ng per gram in PET plastic debris

PCB concentrations were detected in these three samples from three sites submitted for analysis as shown in Fig. 8. Five of the 13 PCBs were detected with a concentration between 0.18 and 1.24 ng/g in the three PET samples submitted for analysis. PCB 18 and 28 are the most abundant. The highest observed concentration of PCBs is PCB 28 with 1.24 ng/g; this concentration is detected at the Fishing Port site.

3.2.4. Sum of PCB concentrations

Figure 9 compares the amount of PCBs found on the three types of plastic debris and on the three sites. At the Aneho site, the total sum of PCB concentrations on LDPE (26.95 ng/g) is three times the sum of PCB concentrations on PP (8.85 ng/g) and slightly more than six times the sum of PCB concentrations on PET (4.04 ng/g). At the Kodjoviakope site, the total sum of PCB concentrations on LDPE is higher (14.61 ng/g) than the sum of PCB concentrations in PP (11.37 ng/g) and the sum of PCB concentrations in PET (1.6 ng/g). On the other hand, at the Fishing Port site, the trend changes. At this site, the sum total of PCB concentrations in PP is in first place with a value of 13.04 ng/g, followed by the sum total of PCB concentrations in LDPE (9.87 ng/g) and 2.74 ng/g in PET. Also, of the three sites, the Aneho site has the highest PCB absorption in LDPE and PET. Taking into account the volume of PCB concentrations on all plastic debris, Aneho is the site with the highest PCB uptake, followed by Kodjoviakope and Fishing Port.

3.3 Determination of pesticides : Concentrations of Pesticides residues in ng per gram in Fishing Port plastic debris

Nine samples from three sites were submitted for analysis. Figure 10 shows that pesticides were identified only at the Fishing Port site. Of the 33 pesticides listed, only two pesticides were detected on the PET plastic samples. These were terbutryn and aclonifen with concentrations of 1.74 ng/g and 0.24 ng/g respectively.

Plastic debris of the LDPE, PP and PET types from the Aneho, Kodjoviakope and Fishing Port sites on which the study is conducted; contain PAH, PCB and pesticide pollutants. This proves that the Togolese coast contains pollutants of this nature. The presence of these pollutants is justified by their transfer from air to water, from soil to water, and from the discharge of wastewater from factories. Indeed, PAH and PCB particles have been found in air masses from Asia and America (Primbs et al., 2008).

The LDPE plastic debris from the three sites showed 15 PAHs, PP debris showed 11 PAHs and PET debris showed 9 PAHs out of 18 reported (Figs. 2, 3 and 4). This abundant presence of PAHs on LDPE compared to PP and PET samples at all sites shows an existing affinity between PAHs and LDPE. Speaking of the polymeric nature, LDPE and PP are all polyolefins while PET is aromatic in nature. However, according to Alimi et al (2018), the sorption capacity of contaminants on LDPE is higher than that of PET. This could explain the abundant adsorption of PAHs by polyolefins to the detriment of PET. Contrary to the results of Rochman et al. (2013) who pointed out that PS adsorbed low molecular weight PAHs more efficiently than PPs, in this study abundant PAH adsorption on PETs should be expected than on polyolefins. Indeed, due to strong hydrophobic interactions generated by the presence of pi (π) bonds in both compounds, PAH sorption should be more abundant on PET than on polyolefins (LDPE and PP). Reconciling the two ideas, it can be stated that the majority of PAHs adsorbed by polyolefins are of high molecular weight. And secondly, it can be estimated that this abundant adsorption may be due to the age of the plastic in the sea. Indeed, it has been proven that plastic in the sea degrades (Hong, 2015 ; Sizing, 2023). Thus, the longer the residence time, the more the plastic degrades. And the more it degrades the more it increases a high surface to volume ratio giving them the ability to adsorb persistent organic pollutants present in the marine environment (Boucher et al., 2016 ; Lee et al., 2013).

The highest concentration of PAHs detected in LDPE plastic debris at all sites was Indeno[1,2,3-cd]pyrene with a value of 110.94 ng/g compared to an average of 11.6 ng/g found in nine (09) samples from the North Atlantic Gyre (Wong-wah-chung, 2019). This type of PAH was not found in the PET samples from the three sites on the Togolese coast, nor in the PET samples from the North Atlantic Gyre. Thus, analysing these results, it can however be said that Indeno[1,2,3-cd]pyrene will be a PAH with high molecular weight since according to research, the partition coefficient of PE-water increases with the molar mass of PAHs (Choi et al., 2013). Another finding was that Naphthalene was found to be the most abundant in PP plastic debris at all sites with an average concentration of 129.83 ng/g compared to an average concentration of 315 ng/g found in five (05) PP samples from the Indonesian coast of Cilacap (Wong-wah-chung, 2019). This result supports the second hypothesis that the abundant PAH adsorption may be due to the age of the plastic in the sea. Indeed, Naphthalene being a low molecular weight PAH should through strong hydrophobic interactions generate the presence of pi (π ) bonds in both compounds to allow abundant sorption of PAHs on PETs.

Also, a critical look at Fig. 5 shows that on the three sites, the highest PAH adsorption on LDPE with an average concentration of 1182.6 ng/g; also on PP (336.57 ng/g) and on PET (274.06 ng/g) is obtained on the Fishing Port site. The Fishing Port is the most polluted site in terms of PAH, followed by Aneho and Kodjoviakope. This can be explained by the geographical location of the Fishing Port on the Togolese coast. Indeed, the fishing port is adjacent to the autonomous port of Lome. Thus, most of the boats that leave other continents and come to the Lome Port emit exhaust gases that constitute a source of PAH. Moreover, these ships transporting oil sources (made up of PAHs) may experience seepage. In addition, the existence of factories in this area whose wastewater discharge also constitutes a source of organic pollutants. The study carried out on plastic granules on Chemu Lagoon beach (Ghana) located near the Tema refinery showed a high concentration of PAHs per granule with a value of 2751 ng/g (Yeo, 2017). This result confirms the influence of maritime traffic and industrialised areas on the fishing port.

The detection of PCB in the nine samples of plastic debris from the three sites showed the same disproportionality that was reported for the detection of PAH. Plastic debris of the LDPE type showed the presence of 11 PCBs, that of the PP type showed 7 PCBs and that of the PET type showed 5 PCBs out of the thirteen notified (Figs. 6, 7 and 8). This difference can be explained by sorption processes. Indeed, highly chlorinated PCBs have a high affinity with PE plastic debris (Wong-wah-chung, 2019). PCB 138 is the most abundant detected on LDPE and PP polymers. On the other hand, in PET samples, the most abundant PCB is PCB 18 with an average concentration of 0.96 ng/g compared to 0.04 ng/g found in three samples from the North Atlantic Gyre. Being of the same polymeric nature, it can be estimated that this difference in concentration is due to the stay of the PET and the different nature of the environments (temperature, salinity and pH). Indeed, an increase in the salinity of the medium and the residence time of the particle generally leads to an increase in sorption (Rochman, 2015 ; Munier, 2018 ; Guo, 2019).

Figure 9 shows that, taking into account the volume of PCB concentrations in all the plastic debris collected at the sites, Aneho is the site with the highest PCB uptake, followed by Kodjoviakope and the Fishing Port. These results obtained slightly biased the arguments made when the Fishing Port was the most polluted site with regard to PAH pollutants. However, given that these sites are on the same coastline, marine currents could shift pollutants from one site to another, especially as the Aneho site is located on the slope of the Fishing Port. In addition, under the same action of marine currents, plastic debris can be transported from one site to another or from one coast to another. Work on microplastics in the Gulf of Guinea region, and in Nigeria in particular, reinforces the point that pollutants vary from coast to coast. In fact, this work has proved the existence of PCBs in concentrations of between 0.00 and 0.53 mg/kg, or in ng/g a value of between 0.00 and 530 (Fred-Ahmadu, 2022). As these two countries are on the same coast, ocean currents can easily carry these PCBs from the Nigerian coast to the Togolese coast.

The study was also able to detect the existence of pesticides. Figure 10 shows that pesticides were identified only at the Fishing Port site. Of the 33 pesticides listed, only two were detected on PET-type plastic samples. These were Terbutryn and Aclonifen, at concentrations of 1.74 ng/g and 0.24 ng/g respectively. This low level of pesticide detection can be explained by the fact that most pesticides photolyse rapidly to give other by-products, since quantities of between 0.04 and 2.02 mg/kg (i.e. 40 and 2020 ng/g) have been found in Nigerian marine ecosystems (Fred-Ahmadu, 2022).

This study allowed the quantification of persistent organic pollutants adsorbed by three types of plastics (LDPE, PP and PET). Thus, nine samples of plastics from three sites were analysed. The analysis indicated the presence of PAHs, PCBs and pesticides. This presence of pollutants is due to the permeable and lipophilic nature of plastic. The analysis also indicated differences in concentration and distribution. In terms of PAH quantity, the Fishing Port site came first, while the Aneho plastic debris is the most polluted with PCBs. This may suggest the degradation of chemicals via ocean currents. These POPs being stable, resistant to chemical and biological degradation, and having bioaccumulative properties are dangerous. For example, benzo(a)pyrene is a carcinogen and deserves a high level of monitoring by political authorities as it was found in samples from all three sites at significant concentrations. The detection of PCBs 52, 101 and 153 along the Togolese coast is a matter of concern for the whole population as these three types of PCBs are among the six European indicators (Jambeck et al., 2015). Terbutryn has the higher concentration of the two pesticides found. It is a pesticide that is hazardous to aquatic organisms and causes long-term adverse effects. The abundance of plastic debris associated with its floating in the sea allows marine fauna to ingest more plastic particles than their natural food. However, the study has now shown that this plastic debris accumulates a number of POPs that are very dangerous for marine organisms and the entire food chain. Indeed, plastic particles have the potential to release POPs once they are ingested.

ACKNOWLEDGEMENTS

Our thanks go to the waste management, treatment and recovery laboratory (GTVD), the regional centre of excellence on sustainable cities in Africa (CERViDA) and the composting platform of the NGO ENPRO. We would also like to thank the General Manager of the fishing port for agreeing to host us at his facility, and all the fishermen who helped us collect the waste.

DECLARATION OF INTERESTS

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Picture 1 and 2 are available in the Supplementary Files section.

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Picture 1 : Type of plastic (a. LDPE; b. PP and c. PET)
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Picture 2 : Samples collected from three sites

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Quantification of PAHs, PCBs and Pesticides adsorbed by plastic waste in the Togolese marine environment

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Abstract

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1. INTRODUCTION

2. MATERIALS AND METHODS

2.1. Presentation of the study site

2.2. Collection of samples

2.3. Experimental procedure

2.3.1. Solvents, Reagents and Chemicals

2.3.2. Extraction

2.3.3. Preparation of standard/stock solutions

2.3.4. Instrument Conditions

2.3.5. Quality Control

3. RESULTS

3.1. Determination of PAHs

3.1.1. Concentration of PAHs in ng per gram in LDPE plastic debris

3.1.2. Concentration of PAHs in ng per gram in PP plastic debris

3.1.3. Concentration of PAHs in ng per gram in PET plastic debris

3.1.4. Sum of PAH concentrations

3.2. Determination of PCBs

3.2.1. Concentration of PCBs in ng per gram in LDPE plastic debris

3.2.2. Concentration of PCBs in ng per gram in PP plastic debris

3.2.3. Concentration of PCBs in ng per gram in PET plastic debris

3.2.4. Sum of PCB concentrations

3.3 Determination of pesticides : Concentrations of Pesticides residues in ng per gram in Fishing Port plastic debris

4. DISCUSSION

5. CONCLUSION

Declarations

References

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Supplementary Files

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