Abstract:
Microplastic (MP) pollution is an emerging concern due to its persistence and ecological
impacts. Mangroves are particularly vulnerable because of their dense roots, high sediment
retention, and proximity to human activities. However, information on vertical MPs
distribution in Sri Lankan mangroves are limited. This study assessed the abundance, vertical
distribution, and morphology of MPs in soils from restored, degraded, and natural
environments at the Accelerated Natural Regeneration of Mangroves (ANRM) site at
Anawilundawa, Sri Lanka., Soil samples were collected at 10 locations, with triplicate samples
at four depth intervals viz., (0-15, 15-30, 30-50, and 50-100 cm). MPs were extracted using
density separation (NaCl), organic matter digestion (10 % KOH and 30% H2O2). Particles were
identified and quantified using a stereomicroscope. Soil physicochemical properties: pH, bulk
density, salinity, electrical conductivity (EC), temperature, and soil colour were recorded
following standard procedures. The highest MP proportion was recorded in the 0-15 cm layer
(39.68 ± 19.0 particles l-1), while the lowest occurred at 50-100 cm (25.18±13.36 particles l-1),
revealing a significant decline with increasing depth. MP abundance differed significantly
among sampling locations (p < 0.001), with canal-associated restored areas showing the highest
contamination (36.0±16.8 particles l-1) followed by other environments. Fibers were the
dominant morphotype (96.7%), followed by films, fragments, foams, and pellets. Blue fibers
constituted the highest proportion (39.6%) among other fiber colours. The results indicate that
mangrove soils at Anawilundawa function as sinks for MPs, with surface accumulation and
evidence of vertical transport into deeper soil layers. These findings highlight the influence of
hydrodynamic processes, particularly canal water flow, on MP distribution and emphasize the
need for improved waste management.
