A systematic review of wet and dry deposition of reactive nitrogen, sulfur, and heavy metals: ecosystem contamination and food chain disruption in Ghana

Environmental contamination in Ghana, driven by dust deposition, particulate matter (PM), reactive nitrogen, sulfur, and heavy metals, poses significant risk to public health and the environment. However, comprehensive assessments of the spatial distribution and seasonal variations of these pollutants remain limited. To address this gap, this study synthesizes data from 68 site-specific studies conducted between 1997 and 2024. Our findings reveal substantial regional disparities in contamination levels. During the Harmattan season, the Northern region accounted for 52% of total dust deposition, while the Central and Southern regions contributed 12% and 37%, respectively. The Central region exhibited the highest concentrations of PM, with median values of PM2.5 (489 μg m⁻³), PM10 (703.5 μg m⁻³), and TSP (710.5 μg m⁻³). Heavy metal contamination in agricultural products was particularly concerning, with cocoa showing elevated levels of copper (48.67 mg kg⁻¹), lead (70.03 mg kg⁻¹), and iron (41.60 mg kg⁻¹). Fish samples revealed high lead (5.97 mg kg⁻¹) and iron (156.39 mg kg⁻¹). Lettuce and onions demonstrated moderate contamination with lead and cadmium. In mining regions such as Obuasi, lead and arsenic concentrations exceeded WHO safety limits. Sulfur deposition was notably high in Southern Ghana, constituting 81.4% of airborne pollutants. Rainwater contamination, primarily from sulfate, contributed to acidic rainfall (pH < 6.5) in the Southern and Central regions. These findings underscore the urgent need for targeted interventions, particularly in mining and urban areas. Implementing stronger pollution control measures, enhancing monitoring systems, and developing specific strategies to mitigate risks to public health and agriculture are critical steps toward addressing these environmental challenges.