**2. Persistent organic pollutants: definition and environmental fates**

Several international environmental organizations, including the Geneva Inter-Organisation Programme for the Sound Management of Chemicals, the United Nations (UN) under its United Nations Environmental Programme (UNEP), the Food and Agriculture Organization (FAO) and the WHO, have described POPs as chemicals that are stable and persist in the environment, bioaccumulate in organisms and the food chain, are toxic to humans as well as animals, and have chronic effects such as the disruption of reproductive, immune and endocrine systems, as well as being

carcinogenic [20–24]. It is believed that these substances can enter the environment through several ways, including release from waste dumps, spillages, industrial and agricultural waste, urban/agricultural runoff and the burning of various materials, thus being distributed in various environmental matrices, including water, air, soils, sediments and living organisms [25–28]. Given the fact that POPs have bioaccumulation potentials and can travel long distances to places far from the points of release by means of waterways, atmospheric exchange and agricultural runoffs, POPs have been detected even in pristine areas such as the Antarctica and the Arctic regions, regions with minimum direct anthropogenic disturbance [25, 28, 29]. In 1997, in order to limit POPs transportation and environmental contamination, the international community decided to work towards the establishment of a convention that would serve as an international, legally binding instrument, to reduce and/or eliminate the release of POPs, as identified in the UNEP Governing Council Decision 19/13C [20]. Consequently, under the Stockholm Convention of POPs (COP-4) for global action, the UNEP, in 1995, listed twelve POPs which are also known as the "dirty dozen", and consisted of Aldrin, dieldrin, dichloro-diphenyl-trichloroethane (DDT), endrin, heptachlor, chlordane, hexachlorobenzene (HCB), mirex, toxaphene, PCDD/ Fs i.e., polychlorinated dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs). In this regard, the Convention's Governing Council took a decision 18/32 to begin investigating POPs, and their persistence in the environment, and thus initiate the eradication or restricted use of these substances, and ultimately minimize the contamination of food chain [28–32].

Moreover, the sources of different POPs have been established. For instance, deliberate application to crops and soils is suggested to be the source of agrochemical POPs, while organochlorine pesticides (OCPs) and other industrial chemicals are reported to be intentionally produced for various uses, for example as flame retardants, as ingredients in consumer products, including electronic goods, which generally result in their unintentional release into the environment, some in the form of e-waste [28, 33–36].

In addition, the use of fire-fighting foams, vehicles and the burning of wood, have been mentioned as potential contributors to POP release into the environment in developing countries [28, 35]. Organic pollutants can enter the coastal environment by several processes and once introduced to this environment, they are subject to biogeochemical cycling, sinking, and other environmental processes [28, 37].

Furthermore, evidence suggests that the low rate of escape of POPs into water reservoirs (i.e., streams), or stock of materials and products, is a source of great concern because it could result in exposure that could cause subtle toxicological effects in humans and biota [38–41]. Similarly, an increasing number of materials containing POPs, are used in building materials, in goods and in various consumer products [42, 43]. For POPs contained in consumer products, their low vapor pressure can result in a slow but significant release into the environment [35] which can come from direct volatilization as well as microscale abrasion of plastics [42, 43]. Following release, the fate of the POP compound in the environment is largely based on its physico-chemical properties and the characteristics of the environment [44].

Besides, it has been suggested that the process of environmental transport of these compounds and their detection into food supplies will be augmented if the compound is in the biosolids applied to agricultural lands, in wastewater effluents discharged to surface waters and in landfills adjacent to agricultural lands, and if industrial facilities that use the compound are located near sources of food [45]. The exposure of infants has also been reported as it becomes evident that POPs can be transferred from mother to infant via breast milk, and umbilical cord serum [46–49].

*Medicinal Plants Threatened by Undocumented Emerging Pollutants: The Sub-Saharan African… DOI: http://dx.doi.org/10.5772/intechopen.103825*

In addition, regardless of the tremendous work that has been done on the African continent regarding reporting and documenting the prevalence of POPs in the African environment over the years [30, 50–53], there is not sufficient evidence on the state of emerging pollutants, such as PFASs, on the continent, compared to the rest of the world; and the reviewed literature has suggested that these undocumented pollutants are a threat to the general African environment [54].

#### **2.1 What are per- and polyfluoroalkyl substances?**

There is no general accepted definition of PFASs. However, PFASs are chemicals that fall under the category of new emerging pollutants, for they exhibit properties which are different from traditional pollutants [28] and were anthropogenically synthesized since 1950s by linking a chain of carbon and fluorine atoms together using two major manufacturing methods, namely electrochemical fluorination (ECF) and telomerization technics [55–60]. PFASs are therefore not present in the environment naturally, but are referred to as "forever chemicals", unlike its counterparts such as heavy metals, e.g., compounds such as arsenic (As), mercury (Hg), lead (Pb), cadmium (Cd), chromium (Cr), etc.

These industrial chemicals (i.e. PFASs) contain at least one perfluoroalkyl fraction and have been previously referred to as "perfluorinated chemicals" (PFCs); albeit "PFCs" being a term describing perfluorocarbons, i.e., substances that contain only carbon and fluorine atoms, and having physical properties, such as being oil and water repellent and temperature resistant and reducing friction, and unique chemical functionalities that are fundamentally different from those of many PFASs [59, 60]. Because of these attributes, PFASs have been largely used as part of feedstocks in several manufacturing processes to make consumer and industrial products [60]. Accordingly, the common uses of PFASs have included: (a) non-stick cookware, stain resistant carpets and fabrics, (b) coatings on some food packaging (e.g., microwave popcorn bags and fast-food wrappers), (c) components of fire-fighting foam, (d) many industrial applications, (e) consumer products—for example, products that are stain and/or water resistant, cosmetics, and some cleaning products [19, 60].

Additionally, a common terminology for the nomenclature of PFASs has thus been agreed upon and saw PFASs divided in two classes, namely non-polymeric and polymeric PFASs [60], each with subclasses, groups and subgroups, as depicted on **Table 1**. For more details, there are various references therein [59–64]. In addition, it is currently estimated that more than 5000 known PFAS chemicals exist, with perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) being the most manufactured; and their numbers are expected to increase as industries continue to invent and manufacture new substances [61, 62]. For instance, in 2006, it was reported that the production of these chemicals reached its peak in China, a major trading sub–Saharan African partner, with more than 250 tons/year [58].

#### **2.2 Reasons behind PFASs attention and how people get exposed to them**

During the last decades, there has been sufficient evidence on the distribution of PFASs in the environment at large, predominantly in the aquatic and biota environments, but most importantly the attention has been on the fact that these substances have been said to be capable of widely spreading [65]. In this regard, the discovery of PFASs in serum, urine and other tissue samples has prompted researchers wanting to know whether these chemicals can lead to health issues [66]. Similarly, studies have


*╬All hydrogen (H) atoms on all carbon (C) atoms in alkyl chain attached to a functional group have been replaced with fluorine (F).*

*╣All H atoms on at least one (but not all) C atoms have been replaced with F.*

*a Manufactured by either ECF or telomerization.*

*b Manufactured by ECF.*

*c Manufactured by telomerization.*

*Adapted from [60].*

#### **Table 1.**

*Per- and polyfluoroalkyl substances family.*

found that PFASs get exposed to in various exposure pathways, including the numerous products to which the application of PFASs led to their manufacturing, thus causing multiple opportunities for exposure. On the other hand, there are already more than 5000 of these compounds available worldwide, and their number is expected to increase. In addition, PFAS's unique properties have also made them stable in the environment and food sources, ultimately making them to be persistent, i.e., that once they enter the environment PFAS remain in the it for an unknown length of period and take many years to leave the body they have entered [66–68]. The other subject of PFAS's attention is their bioaccumulation characteristic [65].

Moreover, it has been argued that all sources of exposure are not conclusively understood [65], but numerous studies have suggested that people are most likely to be exposed to these compounds by means of drinking and consuming PFAS-contaminated water or food, using products made with PFAS, or breathing air containing PFAS [69–75].

The next pressing subjects of attention as far as PFASs are concerned are PFAS precursors (pre-PFAS) and alternatives to PFASs of concerns. Hence, pre-PFASs are formed by means of biotic or abiotic degradation from other PFASs [60, 76], while concerns over the effect of PFASs, mostly PFOA and PFOS, on humans and the environment led to an interest in exploring suitable alternatives to these substances; and ultimately three types of alternatives to PFASs, namely, (i) substances with shorter per- or polyfluorinated carbon chains, (ii) non-fluorine-containing substances and (iii) non-chemical techniques. Further details on some of the commonly known commercial alternatives PFASs and their potential health impacts are available [76–78]. Short-chain PFASs refer to those with five and seven or fewer carbons that are perfluorinated, while long-chain have six and eight or more perfluorinated carbons [77]. Concerns over PFAS alternatives are to be exacerbated by the expansion of world's biggest economies who are continuously manufacturing these chemicals in hundreds of tons per annum. Examples of commonly known and commercially available PFAS alternatives to long-chain PFASs, and which safety has been questioned are available in the literature, for example, see [76].

### *Medicinal Plants Threatened by Undocumented Emerging Pollutants: The Sub-Saharan African… DOI: http://dx.doi.org/10.5772/intechopen.103825*

Moreover, like all other substances that are bioaccumulative, persistent and toxic in nature, PFASs have been reported to have the potential to cause health problems. As such, epidemiological evidence has suggested associations between perfluoroalkyl exposure and several health outcomes in humans and animals, even though causeand-effect relationships for humans' cases have remained inconclusive, which have


*Short-chain PFASs are shown in bold type. Italic and bold are plants that are likely to be find in selected supermarkets in sub-Saharan Africa, but which are only produced in selected countries of the region (e.g., South Africa and Namibia).*

*n/i: not indicated.*

*Adapted from [80].*

#### **Table 2.**

*Bioaccumulation of PFASs in edible plants.*

implied that more studies are still needed. There are further details on the toxicological profile of perfluoroalkyls [79].

#### **2.3 Prevalence and bioaccumulation of PFASs in plants**

PFASs are highly soluble in water, a characteristic that make them to be easily absorbed and translocated in plants. This has become a great centre of interest for researchers wanting to comprehend the phytotoxicity of PFASs. Subsequently, during the recent years, there has been an increase in studies that investigate the prevalence and bioaccumulation of PFASs by plants, including cereals, fruits and vegetables. Thus, high concentration levels of PFASs have been frequently reported in plants near contaminated sites [80–84]. The predominant PFASs have been PFOA, perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), and perfluorobutanesulfonic acid (PFBS) in most cases [83–85]. **Table 2** depicts the bioaccumulation of these PFASs in select cereal, fruits and vegetables, some of which are consumed by Africans but not produced locally. It is worth mentioning that the prevalence of these substances in these plants implies exposure to PFASs through the consumption of these crops. More studies are thus required, in this regard, to substantiate this potentiality.
