A review on levels of polychlorinated naphthalenes in matrices with emphasis on knowledge and research gaps priorities in Africa

Polychlorinated naphthalenes (PCNs) were listed as Persistent organic pollutants in the Stockholm Convention, in May 2015, because of their adverse health and environmental effects. PCNs production began in the early 1900s when they were used extensively in several consumer goods as fire retardants. However, because of their health and environmental implications, the production and use of PCNs chemicals were voluntarily banned in many countries in the 1970s and 1980s. However, PCNs are still detected in different environmental samples including air, water, sediments, soil, indoor dust, biota, consumer products, human diet, blood and serum today, as a result of their historical use and unintentional production. Thus, PCNs can be released into the environment throughout their life cycle. It becomes, therefore, crucial to monitor them in different environmental compartments. To date, about 163 reports on PCNs levels in several matrices have been published in different parts of the world. It was reported that toxic PCNs such as chloronaphthalenes 66, 67 and 73 are prevalent in most samples; thus, there is a need to continuously monitor these congeners in our environment. However, there are sparse studies related to PCNs levels, not only in consumer products, leachates and sediment samples from landfill sites in Africa but also in other matrices, leaving a huge research gap that must be prioritized. To date, only about 3 studies on PCNs have been published in Africa, bearing in mind that there is no documented evidence of any known production of PCNs in the continent. Thus, a wide research gap in PCNs studies still exists in Africa. There is an urgent need, therefore, to conduct studies and establish robust PCNs inventories in Africa. The present review examines the existing knowledge on PCNs levels and trends in Africa, and identifies research gaps that ought to be addressed so that the scale of PCNs distribution in the global environment can be known.