Variation in heavy metals concentrations among seaweed species from Mkwiro seaweed farm, Kwale County, Kenya

Abstract

This study, conducted at the Mkwiro seaweed farm in Kwale County, Kenya, aimed to assess the concentrations of heavy metals (Cd and Pb) and essential elements (Na, Fe, Ca, and K) in selected edible seaweed species. The study used a cross-sectional, descriptive research design and probability sampling method to collect data. Seaweed samples of three selected species, Cottonii (Kappaphycus alvarezii), Sea lettuce (Ulva lactuca), and Bubble-green seaweed (Boergesenia forbesii) were collected in quadrants and subjected to chemical analysis. Statistical analyses were conducted using R Studio version 4.3.2, with a significance level set at α=0.05. The Kruskal-Wallis test revealed significant differences in lead concentrations among seaweed types (χ² (2) = 7.01, p = 0.03). Cadmium concentrations did not show significant differences (χ² (2) = 3.88, p = 0.14). For calcium concentrations, ANOVA indicated no significant effect of seaweed type (F (2,33) = 0.6381, p = 0.5347). Iron concentrations differed significantly among seaweed types (χ² (2) = 23.35, p = 0.00000849), with B. forbesii having the highest median concentration. Potassium and sodium concentrations did not significantly vary among seaweed types (p > 0.05). The study uncovers elevated cadmium levels in seaweed, indicating potential contamination risks. However, concentrations of essential elements were lower. To address these findings, it is recommended to initiate regular monitoring and pollution control measures in seaweed farms. Additionally, diversifying cultivation with low-metal species can enhance product safety and quality.