Abstract:
Non-target organisms, including human and wildlife, are susceptible to deleterious effects of pesticide mixtures in their environment. Present study demonstrated the disruption of the hypothalamic-pituitary-thyroid (HPT) axis in a seasonally breeding wildlife bird Amandava amandava on co-exposure to dithiocarbamate mancozeb/MCZ and neonicotinoid imidacloprid/IMI, at concentrations even lower than respective environmentally realistic exposure level of each of the pesticide. Adult male birds (n=8/group) were exposed individually to 0.25% LD50 of each of MCZ (0.14mg) and IMI (2.75μl) followed by co-exposure to their equimixture as MIX-I (0.25% LD50 of each) and MIX-II (0.5% LD50 of each) through food for 30d in preparatory phase of reproductive cycle. Disruptions of thyroid gland and pituitary-thyroid axis were evident. Altered thyroid weight and volume, follicles with inactive colloids and lesions, decrease of height and nucleus-to-cytoplasm ratio of follicular epithelial cells were noted. Plasma levels of T4 and T3 were decreased, more significant in mixture groups than in individually exposed groups. Within co-exposed groups, comparatively high plasma T4 and T3 levels in MIX-II than MIX-I indicated dose non-responsiveness of the pesticides in mixtures; a characteristic displayed by endocrine disrupters. Plasma TSH level was increased in MCZ- and IMI- but decreased in MIX-I and MIX-II suggesting the disruption of the negative feedback and impairment of the HPT axis in co-exposed groups. Effects were more prominent in co-exposed groups due to combinatorial action and cumulative toxicity of pesticides. Considering the role of thyroid hormones in reproductive development, pesticides even in low dose could affect the thyroid homeostasis and reproductive axis.
摘要:
非目标生物,包括人类和野生动物,容易受到环境中农药混合物的有害影响。本研究表明,在季节性繁殖的野生鸟类Amandavaamandava中,下丘脑-垂体-甲状腺(HPT)轴的破坏与二硫代氨基甲酸酯代森锰锌/MCZ和新烟碱类吡虫啉/IMI共同接触,浓度甚至低于每种农药各自的环境现实暴露水平。成年雄性鸟类(n=8/组)分别暴露于MCZ(0.14mg)和IMI(2.75μl)各自的0.25%LD50,然后在生殖周期的准备阶段通过食物将其共同暴露为MIX-I(每个的0.25%LD50)和MIX-II(每个的0.5%LD50)30天。甲状腺和垂体-甲状腺轴的破坏明显。甲状腺重量和体积改变,有不活跃胶体和病变的卵泡,注意到滤泡上皮细胞的高度和核质比降低。血浆T4和T3水平降低,在混合组中比在单独暴露组中更显著。在共同暴露的群体中,与MIX-I相比,MIX-II中的血浆T4和T3水平相对较高,表明混合物中农药的剂量无反应性;内分泌干扰物显示的特征。血浆TSH水平在MCZ-和MI-中升高,但在MIX-I和MIX-II中降低,表明在共同暴露组中负反馈的破坏和HPT轴的损害。由于农药的组合作用和累积毒性,共同暴露组中的影响更为突出。考虑到甲状腺激素在生殖发育中的作用,即使低剂量的农药也会影响甲状腺稳态和生殖轴。