氨基甲酸酯类农药对蛋白核小球藻联合毒性作用特点及机制

氨基甲酸酯类农药广泛应用于农业生产中,其在环境中的残留及其对非靶标生物的毒性作用引起关注。以5种氨基甲酸酯类农药包括残杀威、灭多威、抗蚜威、涕灭威和呋喃丹为研究对象,以蛋白核小球藻为受试生物,应用微板毒性分析法系统测定每种农药及其五元混合物对蛋白核小球藻在不同暴露时间(12、24、48、72和96 h)的生长抑制作用,并同步分析农药对蛋白核小球藻的生理特性如叶绿素含量、蛋白质含量、超氧化物歧化酶(SOD)活性和脂质过氧化物丙二醛(MDA)含量的影响。结果表明,5种农药对蛋白核小球藻的浓度-效应均具有明显的时间依赖性,农药抗蚜威在中低浓度促进绿藻生长,呈现非单调J型浓度-效应曲线(CRC)特征,其余4种农药的CRC呈现经典S型;以半数效应浓度的负对数(p EC50)为毒性大小指标,5种农药在96 h时毒性大小为:呋喃丹(p EC50=3.43)残杀威(p EC50=2.76)抗蚜威(p EC50=2.12)灭多威(p EC50=2.11)涕灭威(p EC50=1.89)。浓度为EC50的5种农药处理后的蛋白核小球藻中叶绿素和蛋白质含量随暴露时间的延长而减少,但不同农药处理的绿藻中叶绿素和蛋白质含量减少率随暴露时间延长变化趋势稍有不同; SOD酶活性随着暴露时间延长逐渐下降,MDA含量逐渐增加,这说明藻细胞受到破坏,脂质过氧化的损害程度超过细胞修复能力,SOD活性被抑制,细胞的抗氧化能力下降,藻细胞内的H2O2不断积累,导致MDA含量升高。五元混合物对蛋白核小球藻的毒性也具有一定的时间依赖性,并表现出刺激作用,即hormesis现象,且混合物毒性与组分浓度比具有良好的线性相关性;暴露于混合物的小球藻均在96 h出现了刺激效应,其叶绿素与蛋白质含量随暴露时间延长不断增加,SOD活性不断升高,MDA含量不断减少;五元混合物均在96 h呈现出拮抗作用,且与混合物的浓度和组分浓度比相关。

Time-dependent Joint Toxicity Characteristics and Mechanisms of Five Carbamate Pesticides towards Chlorella pyrenoidosa

Carbamate pesticides are widely used in agricultural production, so their residues in the environment and toxicity towards non-target organisms are concerned. Five kinds of carbamate pesticides, i.e. baygon, pirimicarb, methomyl, aldicarb and carbofuran were selected as research substances, the microplate toxicity analysis method was used to determine the growth inhibition toxicity of each pesticide and their mixtures towards Chlorella pyrenoidsa in different exposure times (0, 24, 48, 72 and 96 h). The effects of the five pesticides and their mixtures on the physiological characeristics such as chlorophyll content, protein content, superoxide dismutase (SOD) activity and lipid peroxidation product malondialdehyde (MDA) content in Chlorella pyrenoidosa were also investigated to explore possible toxicity mechanisms. The results showed that the five pesticides had time-dependent effects. The pesticide pirimicarb promoted the growth of green algae at low and medium concentrations, showing a non-monotonic J-type concentration-response curve (CRC). The CRCs of the other four pesticides showed classic S types. Selecting the negative logarithm of the half effect concentration (pEC₅₀) as the toxicity index, toxicity order of the five pesticides in 96 h was as follows: carbofuran (pEC₅₀=3.43) > baygon (pEC₅₀=2.77) > pirimicarb (pEC₅₀=2.12) > methomyl (pEC₅₀=2.11) > aldicarb (pEC₅₀=1.89). The chlorophyll and protein contents as well as SOD activity in Chlorella pyrenoidosa decreased gradually with the lengthening of exposure time. However, MDA contents increased with time lengthening, showing that the algae cells were destructed and the lipid peroxidation exceeded the self-repairing ability of the cells. This caused the inhibition of SOD activity, and thus harmed the antioxidant capacity of cells. Thus, the accumulation of H₂O₂ in algae cells resulted in the decreasing of SOD activity and increasing of MDA content. Toxicity of the five pesticide mixtures was also time-dependent and showed stimulatory effect, i.e. hormesis phenomenon. The maximum stimulating effects of the five-component mixtures appeared in 96 h, and the chlorophyll and protein content together with SOD activity also increased. As a result, the content of MDA was continuously decreased. Antagonism appeared in the five-component mixtures in 96 h, which was closely related to the concentrations or concentration ratios of mixture components.