Influence of humic acid and fluvic acid on the altered toxicities of arsenite and arsenate toward two freshwater algae

• Published in: Aquatic toxicology 2022-08, Vol.249, p.106218-106218, Article 106218
• Main Authors: Wang, Ning-Xin, Chen, Zheng-Yu, Zhou, Wen-Qiang, Zhang, Wei
• Format: Article
• Language: English
• Subjects: Arsenic toxicity; Bioaccumulation; Biotransformation; Freshwater algae; Fulvic acid; Humic acid
• ISSN: 0166-445X; 1879-1514
• DOI: 10.1016/j.aquatox.2022.106218

•Without DOM, AsV was more toxic than AsIII to C. reinhardtii; AsV was less toxic than AsIII to O. danica.•DOM had opposite effects on AsV and AsIII toxicities in both species via different bioaccumulation patterns.•The algae O. danica had a faster biotransformation ability of AsV and AsIII than C. reinhardtii.•Combined inorganic arsenic and DOM helps estimate the environmental risk of arsenic. Arsenic pollution in freshwater poses a serious threat to aquatic organisms. However, dissolved organic matter (DOM) in water can modulate arsenic environmental toxicity by either suppressing or promoting its bioaccumulation. In this study, we investigated the toxicity, bioaccumulation, and biotransformation of inorganic arsenic (arsenite AsIII and arsenate AsV) combined with two types of DOM, i.e., humic acid (HA) and fulvic acid (FA), in the algae Chlamydomonas reinhardtii and Ochromonas danica. C. reinhardtii has a cell wall and cannot bioaccumulate arsenic complexation, whereas O. danica has no cell wall. Without DOM, AsV was more toxic than AsIII for C. reinhardtii, and AsV was less toxic than AsIII for O. danica. HA and FA addition reduced AsV and AsIII toxicities; the larger molecular weight (Mw) of HA contributed to the reduction in toxicity to an even greater extent, and reduced arsenic accumulation while promoting the biotransformation ability of C. reinhardtii, which has a cell wall. However, HA and FA addition increased AsV and AsIII toxicities and arsenic accumulation while relatively enhancing the biotransformation ability of O. danica, which has no cell wall. Coupling toxicity, bioaccumulation, and biotransformation, DOM (HA and FA) contributed to the altered toxicity of freshwater algae to AsV and AsIII through reduced/increased arsenic accumulation and enhanced biotransformation. Overall, our study considered the combined toxicity of inorganic arsenic and DOM in phytoplankton, helping estimate the potential environmental risk of arsenic in aqueous environments.