Acesulfame K and p-arsanilic acid impair rice seed germination and seedling growth: A bitter-sweetener, perilous symphony

The widespread use of additives introduces emerging contaminants, including acesulfame (ACE) and p-arsanilic acid (p-ASA), into agricultural systems, where their co-occurrence may affect crop development. This study investigated the individual and combined effects of ACE and p-ASA on rice during early growth. Rice seeds were exposed under controlled conditions to ACE (0.5–50 μM) and p-ASA (10 μM), either individually or in combination. Germination was assessed after 4 and 7 d, whereas biomass and physiological and biochemical responses, including α-amylase, β-amylase, soluble protein, superoxide dismutase (SOD), peroxidase (POD), and malondialdehyde (MDA), were evaluated after 14 d. After 4 d, ACE alone caused small, non-significant reductions in germination, whereas only the highest combined exposure (50 μM ACE + 10 μM p-ASA) significantly reduced germination relative to the control. After 7 d, germination rates ranged from 97.22 ± 3.90% to 99.44 ± 1.36%, with no significant differences among treatments, indicating that the initial co-exposure effect was transient. In contrast, seedling biomass was inhibited by up to 22.05% after 14 d, with inhibition increasing with ACE concentration. ACE alone generally increased enzyme activities and MDA levels while reducing soluble protein content. Co-exposure to p-ASA reduced α-amylase, β-amylase, and POD activities below control levels while increasing SOD activity and MDA accumulation. A higher-than-additive increase in MDA was observed only at the highest combined exposure, indicating enhanced lipid peroxidation, whereas lower ACE concentrations produced additive effects. Overall, ACE and p-ASA had limited and transient effects on germination but impaired seedling growth and altered enzymatic and oxidative-stress responses. These findings demonstrate that the effects of contaminant mixtures are strongly concentration dependent and cannot be inferred solely from the responses to the individual compounds.