Epiphytic Vascular Cryptogams as Bioindicators of Atmospheric Heavy Metal Pollution in Eket Wetlands, Nigeria

Abstract

This study investigates the bioaccumulation of heavy metals in epiphytic vascular cryptogams as indicators of atmospheric pollution in Eket wetlands, Nigeria. The research assessed seasonal variations in heavy metal concentrations of Nephrolepis biserrata, Nephrolepis undulata, and Selaginella myosurus across different sites. Epiphytic plants were obtained from each site using systematic sampling method and analysed for heavy metals. Atmospheric heavy metal analysis revealed that Atabong recorded the highest concentrations of cadmium (0.94 ± 0.12 mg/kg wet season, 0.63 ± 0.00 mg/kg dry season), copper (3.62 ± 0.20 mg/kg wet season, 1.24 ± 0.03 mg/kg dry season), and chromium (5.83 ± 0.16 mg/kg wet season, 4.32 ± 0.58 mg/kg dry season), suggesting significant industrial and vehicular emissions. Lead concentrations peaked at Marina (2.72 ± 0.43 mg/kg dry season), indicating marine-based pollution sources. Heavy metal accumulation in ferns varied significantly across species and locations. N. biserrata exhibited the highest uptake of zinc (31.49 ± 2.27 mg/kg wet season at Atabong) and iron (19.40 ± 1.83 mg/kg wet season at Atabong). S. myosurus recorded the highest cadmium accumulation (4.51 ± 0.16 mg/kg dry season at Atabong), with a bioaccumulation factor of 7.16, highlighting its strong potential for biomonitoring cadmium contamination. The bioaccumulation factors for zinc, copper, and iron were highest in the wet season, suggesting increased metal mobility due to precipitation. Also, spatial analysis revealed that Atabong had the most severe contamination, with consistently elevated heavy metal concentrations across all measured parameters, while Ikot Udota and Etebi exhibited lower pollution levels. The results underscore the effectiveness of epiphytic ferns as bioindicators for monitoring atmospheric heavy metal pollution in wetland ecosystems. The study recommends integrating fern-based biomonitoring strategies into environmental policies and enforcing stricter pollution control measures to mitigate industrial emissions in Eket wetlands.