Investigating the Efficiency and Toxicity of Biochar Adsorption of Aqueous Pesticides and Metals on Daphnia Spp.

Harrison, Idorenyin and Semple, Kirk and Zhang, Hao (2024) Investigating the Efficiency and Toxicity of Biochar Adsorption of Aqueous Pesticides and Metals on Daphnia Spp. PhD thesis, Lancaster University.

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Abstract

The increase in the frequency and extent of aquatic pollution by pesticides and metals remains a serious worldwide problem, largely due to anthropogenic industrial activities since the latter half of the nineteenth century. Pesticides and heavy metals, which are frequently reported to exceed regulatory limits, have direct and indirect impacts on the aquatic ecosystem, pose environmental and health risks to humans and animals, and are more prevalent in developing countries than in their developed counterparts. Biochar, a well-studied and established carbonaceous soil amendment, has recently been investigated as a viable adsorbent for water pollutants. This thesis evaluates the aqueous adsorption of Isoproturon (IPU) by biochar derived from agricultural wastes: rice husk (RH), hardwood (HW), and coconut shells (CS), compared with commercial activated carbon. Secondly, the acute toxicity of untreated and carbon-amended (0.001 -10 mg L⁻¹) IPU, cypermethrin (CP), and the heavy metals arsenic (As), cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) on D. magna and D. pulex over 72- 96 h without feeding, decreased in the order: Ni > Cd ≈ Cu≈ As > Zn > Pb. . Thirdly, the acute toxic effects of biochar treatment of CP, IPU, As, and Cd on the percentage and cumulative CO2 production of D. pulex were studied. Integrating LD₅₀, EC₅₀, and condition index analyses in the evaluation of Daphnia ecotoxicity suggests that the toxicity of all tested pesticides and metals followed the decreasing order Cypermethrin > Cadmium ≈ Copper > Zinc ≈ Nickel > Lead >Arsenic > Isoproturon. This ranking reflects both acute and chronic toxicity patterns observed in the experiments. The overall findings reveal that the adsorption capacities for IPU were in the decreasing order: PAC (97%) > RH biochar (91%) > HW biochar (68%) > GAC (67%) > CS biochar (33%). RH-biochar adsorption of IPU was higher than that of GAC. The respiration of D. pulex in treated and untreated pesticide and metal solutions was significantly affected by the bioavailability of the pollutants, their mode of action on the organism, and the organism's ability to acclimatize to these effects. Furthermore, although biochar amendment of the solutions reduced their toxicity, it also reduced the oxygen levels. This suggests that biochar treatment of water in closed systems could lead to synergistic toxicity between hypoxia and the compounds present. Finally, CP was approximately 100-fold more toxic than IPU, and D. pulex was about 10-fold more sensitive to both pesticides than D. magna, which showed higher resistance to the toxic effects of all pollutants tested except As, Cd, and Zn. RH-biochar is an effective and promising adsorbent for removing pesticides and heavy metals from aquatic systems and could be an environmentally friendly, cost-effective, and efficient technology, but further research is needed to determine production parameters that suit the pollutant types it is intended to treat.