“Green” carbon dots from coffee waste for adsorption of xenobiotic and trace heavy metals in both aquatic and physiological media

Abstract

Xenobiotic and trace heavy metals such as Pb²⁺, Cd²⁺ and Cu²⁺, which abundantly pollute the environment, are hazardous neurotoxicants. Herein, the ability of “green” carbon dots from coffee waste (CCDs) to adsorb Pb²⁺, Cd²⁺ and Cu²⁺ in aquatic media and in biological systems, such as presynaptic rat cortex nerve terminals, was assessed. Using ICP-MS and DLS, it was demonstrated that CCDs were able to adsorb Pb²⁺, Cd²⁺ and Cu²⁺ in water, forming complexes with these metals. In animal experiments, CCDs, even at a high concentration of 2 mg ml⁻¹, did not change the extracellular levels of the excitatory neurotransmitter L-[¹⁴C]glutamate and inhibitory one [³H]GABA in nerve terminal preparations, and so, CCDs are highly biocompatible. Combined application of CCDs with Pb²⁺, Cd²⁺ and Cu²⁺ resulted in a significant mitigation of the acute Pb²⁺/Cd²⁺/Cu²⁺-induced increase in the extracellular levels of L-[¹⁴C]glutamate and [³H]GABA in nerve terminal preparations. Therefore, CCDs did not possess neurotoxic effects and, due to their original synthesis methodology, were able to adsorb Pb²⁺, Cd²⁺ and Cu²⁺ in aquatic media and in biological systems, mitigating acute Pb²⁺/Cd²⁺/Cu²⁺-induced neurotoxicity in nerve terminals. CCDs have prophylactic and therapeutic potential to combat heavy metal poisoning. This study fits several key priorities in environmental science as a heavy metal adsorbent obtained from biowaste using an eco-friendly synthesis protocol has the potential to combat heavy metal poisoning in organisms and wastewater.