Effect of humic acid on prometryn bioaccumulation and the induction of oxidative stress in zebrafish (Danio rerio)

Abstract

Humic acid (HA) is the main component of dissolved organic matter in aquatic ecosystems and affects the bioavailability of contaminants. Prometryn is frequently used to control annual broadleaf and grass weeds and has been widely detected in the aquatic environment. An experiment was conducted to investigate the effect of HA on the chronic toxicity of prometryn in zebrafish. In zebrafish treated with 53.2 μg L⁻¹ prometryn (P), prometryn with 5 mg L⁻¹ HA (P + HA₅), or prometryn with 15 mg L⁻¹ HA (P + HA₁₅), catalase (CAT) activity and glutathione (GSH) content in the visceral mass initially increased and then decreased with exposure time. After one day of exposure, malondialdehyde in the visceral mass increased by 58% to 64% in fish treated with prometryn and HA compared to those treated with prometryn alone, however, this difference disappeared during days 10 to 40. Treatment with HA enhanced the bioaccumulation of prometryn by 34% and 40% on day 1 in the P + HA₅ and P + HA₁₅ groups, respectively, possibly due to changes in gill membrane permeability. Nevertheless, the opposite result was observed during days 10 to 40, owing to the presence of more excreta and suspended particulate matter resulting in a reduction in the quantity of free dissolved prometryn in the P + HA₅ and P + HA₁₅ groups. There were significant correlations between CAT activity and prometryn concentration (0.562**, P < 0.01) and between GSH and prometryn concentration (0.808**, P < 0.01) throughout the first 20 days of the experiment, suggesting a role for these antioxidant systems in the detoxification of prometryn in zebrafish.