Page - 107 - in Freshwater Microplastics - Emerging Environmental Contaminants?

found thatMPdensities ingeneraldidnot significantlyvarybetweensites ineither matrix.Aswith the study conducted 25years prior, the conclusionwas thatwater circulation rather than proximity to land-based sources was main driver to MP abundances in coastal regions [31]. Biological sampling in this region has also revealed a number of interesting details regarding the fate ofmarine plastics. Plastic particles were found inmore than half the seabirds predominantly sampled off Southern Africa and African sector of the SouthernOcean [32]. The size of the ingested particles was related to the body size of the bird, and smaller species exhibited a higher incidence of plastic ingestion.Dark-coloredparticlesweremoreabundantsuggestingaselection for easily visible particles rather than transparent ones. Omnivorous specieswere themost likely toconfuseplasticswithpreyitems,whereasfeedingspecialistswere less likely tomistake plastics for food, unless they shared a resemblance [32]. A comparisonof thishistoricdatasetwithamorerecentsamplingperiod(1999–2006) revealedadecrease invirginpellet ingestion, but nooverall change in total plastic ingestion [33]. This decrease suggested a change in themake-up of small plastic debris at sea in the interveningperiod. Studies in the estuarine environment are less common thanmarine studies and, like freshwater research onMPs, have only recently started to gain momentum. However, estuaries provide pathways for the transport ofMPs fromcatchments to the oceans, notably in urban areaswhere estuarinewaters serve as industrial out- flows or fishing grounds [34, 35]. The characterization of MPs in five urban estuaries of Durban (KwaZulu-Natal, SouthAfrica) found the highest concentra- tions in sediments collected from Durban harbor, which included cosmetic microbeads and fibers [35]. Possible sources were thought to include the several rivers that flow through Durban’s industrial suburbs and enter the harbor, the industrial companies that use plastic powders and pellets around the harbor, and the closeness of drydockswhere ship repairs takeplace.The fate of these plastics was revealed in a follow-up studyby the sameauthors looking at plastic ingestion by the estuarinemullet (Mugil cephalus) in Durban harbor [36]. Plastic particles werefoundinthedigestive tractsof73%ofthesampledfish,withmorethanhalfof the recovered plastics in the form of fibers and approximately one-third as frag- ments. Plastic concentrations found in themulletwere higher than those reported elsewhere for other species, and it appears that, aswith omnivorous seabirds, the nonselective feeding mode ofM. cephalus (i.e., ingestion of sediments) was a contributing factor. Studies intoSouthAfrica’splasticandMPpollutionareparticularlypertinentas the country is ranked within the top 20 counties with the highest mass of mismanaged plastic waste [37]. Other African countries are also on the list, and although focused on marine debris, the relevance to freshwaters should not be ignored. Microplastics in InlandAfricanWaters: Presence, Sources, andFate 107