Modulation of phytotoxic and cytogenetic effects of cadmium by humic acid: Findings from a short-term plant-based bioassay

Abstract

The study of the modulation of the toxicity of heavy metals by coexisting chemicals in the environment is vital for realistic ecological risk assessment. Our study was aimed at determining possible toxicity modulations of Cd by humic acid (HA) using the Allium cepa test system. A. cepa bulbs were exposed to Cd (1 and 5 mg/L) and HA (10 mg/L) individually or in mixtures. The root lengths of the bulbs and cytogenetic endpoints in root meristematic cells, including the mitotic index (MI), nuclear abnormalities (NAs), and chromosomal abnormalities (CAs), were determined. The results revealed that the MIs of A. cepa co-exposed to HA and Cd were significantly recovered by >15% compared with those of A. cepa subjected to Cd-only treatments, and this response was more sensitive than the phytotoxic response (root length). Furthermore, the burden of NAs was significantly decreased in the co-exposed bulbs by >20% compared with bulbs with Cd-only treatments. The frequencies of CAs were also reduced in the bulbs co-exposed to HA and 1 and 5 mg/L Cd by >15 and >25%, respectively, compared with bulbs receiving Cd-only treatments. Therefore, our findings indicated that HA plays a significant protective role in Cd toxicity in A. cepa. HIGHLIGHTS Allium cepa was used to determine the modulation of Cd toxicity by humic acid using microscopic and macroscopic endpoints.; Humic acid induced the recovery of the inhibited mitotic index and root lengths caused by Cd stress.; The burdens of nuclear and chromosomal abnormalities were alleviated by humic acid.; Humic acid plays a protective role against Cd toxicity in the A. cepa test system.;

Keywords

• allium cepa
• co-exposure
• heavy metals
• humic substances
• mixture toxicity