The fungicide thiram alters the embryo-larval development of the black sea urchin Arbacia lixula by inducing multifactorial toxicological responses

Thiram, a dithiocarbamate fungicide widely used in agriculture, poses environmental risks to non-target marine organisms due to its persistence in aquatic ecosystems. This study investigates the impact of thiram on the embryo-larval development of the black sea urchin Arbacia lixula, a sensitive model organism in ecotoxicology. A. lixula fertilized eggs were exposed to increasing concentrations of thiram (0.24 to 30 μg/L) for 72 hours post-fertilization (hpf), and dose-dependent morphological alterations, developmental delays, and mortality were observed at both 48 hpf pluteus and 72 hpf ampol-like stages. Generalized Linear Models (GLMs) revealed a thiram Effect Concentration (EC 50 ) of 2.76 μg/L and a Lethal Concentration (LC 50 ) of 26.42 μg/L, with a Teratogenic Index (TI) of 9.57 and a Lowest Observed Effect Concentration (LOEC) of 0.24 μg/L, indicating a marked teratogenic potential of thiram. Gene expression analysis revealed up-regulation of biomarkers related to skeletogenesis (MSP130 and SM30) and endocrine regulation (DIO1), revealing biomineralization impairment and potential modulation of TH-like developmental pathways, respectively. Biochemical assays revealed onset of oxidative stress-related enzymatic responses due to altered enzymatic activities of glutathione S -transferase (GST) and catalase (CAT), besides possible impairment of cholinergic-related processes due to reduced acetylcholinesterase (AChE) activity. Metabolomic profiling by 1 H NMR spectroscopy confirmed the altered skeletogenesis, redox imbalance, AChE modulation, and disrupted energy metabolism, as also supported by the metabolic pathway network and enrichment investigation. These findings suggest that thiram acts as a multifactorial toxicant and possible interference with thyroid hormone-like signaling, highlighting the vulnerability of marine organisms at their early life stages to sublethal chemical exposures, and underscoring the need for stricter environmental monitoring.