FitzPatrick Institute of African Ornithology, DST-NRF Centre of Excellence, University of Cape Town, Rondebosch 7701, South Africa.
FitzPatrick Institute of African Ornithology, DST-NRF Centre of Excellence, University of Cape Town, Rondebosch 7701, South Africa.
Environ Pollut. 2018 Jul;238:1008-1016. doi: 10.1016/j.envpol.2018.02.017. Epub 2018 Feb 16.
Identifying the sources of small plastic fragments is challenging because the original source item seldom can be identified. South Africa provides a useful model system to understand the factors influencing the distribution of beach litter because it has an open coastline with four equally-spaced urban-industrial centres distant from other major source areas. We sampled mesodebris (∼2-25 mm) at 82 South African beaches in 1994, 2005 and 2015. Plastic items comprised 99% by number and 95% by mass of litter items. Industrial pellets were the most abundant plastic items, but fragments of rigid plastic items comprised most of the mass of debris. Strong correlations between industrial pellets and other plastic items indicate that common factors influence the distribution of both pellets and secondary mesoplastics. The abundance of mesodebris at beaches also was correlated in successive surveys, suggesting that beach-specific factors (e.g. aspect, slope, local currents, etc.) influence the amounts of debris on each beach. Sample year had no effect on mesodebris abundance, indicating that there has been little change in the amounts of mesodebris over the last two decades. There were consistently higher densities of both industrial pellets and other plastic items at beaches close to urban-industrial centres; there were only weak correlations with human population density and no correlation with local runoff. The size of industrial pellets decreased away from local urban centres, further supporting the conclusion that, like macroplastic litter, most mesoplastic pollution on continental beaches derives from local, land-based sources. This finding means that local actions to reduce plastics entering the sea will have local benefits, and that it may be possible to assess the efficacy of mitigation measures to reduce marine inputs of mesoplastic items.
确定小塑料碎片的来源具有挑战性，因为原始来源物品很少能够被识别。南非为理解影响海滩垃圾分布的因素提供了一个有用的模型系统，因为它拥有一段开放的海岸线，且有四个均匀分布的城市-工业中心，远离其他主要的源区。我们于 1994 年、2005 年和 2015 年在南非 82 个海滩采集了中碎屑（~2-25mm）。塑料物品在数量上占垃圾物品的 99%，在质量上占 95%。工业颗粒是最丰富的塑料物品，但刚性塑料物品的碎片构成了大部分碎屑的质量。工业颗粒与其他塑料物品之间的强相关性表明，共同的因素影响颗粒和次生中塑料的分布。连续调查中海滩上的中碎屑丰度也存在相关性，这表明海滩特定因素（如方位、坡度、局部水流等）影响每个海滩上的碎屑量。样本年份对中碎屑丰度没有影响，这表明在过去二十年中，中碎屑的数量几乎没有变化。靠近城市-工业中心的海滩上，工业颗粒和其他塑料物品的密度始终较高；与人口密度的相关性很弱，与当地径流量没有相关性。工业颗粒的粒径从当地城市中心向外逐渐减小，进一步支持了这样的结论，即与宏塑料垃圾一样，大陆海滩上的大部分中塑料污染源自当地的陆源。这一发现意味着减少进入海洋的塑料的地方行动将带来地方效益，并且评估减少中塑料进入海洋的缓解措施的效果可能是可行的。
