铜和草甘膦对蚯蚓的毒性效应研究
Cu and glyphosate toxicity to earthworm (Eisenia fetida)
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摘要: 污染物的交互作用及其生态毒理效应已成为环境科学研究的主要方向。含铜杀菌剂与除草剂草甘膦N-(膦酸甲基)甘氨酸是农业生产中常见的农药, 其在土壤中共存可能造成复合污染。草甘膦中含有羧基、氨基、磷酸基等配位基团对重金属阳离子和有机阳离子有很强的络合能力, 草甘膦可以影响重金属的生物有效性、毒性以及重金属在生物体内的积累。本文以赤子爱胜蚓(Eisenia fetida)为例, 采用室内模拟试验, 单一试验设置5个铜浓度25 mg·kg-1、50 mg·kg -1、100 mg·kg-1、200 mg·kg-1和400 mg·kg-1, 5个草甘膦浓度 25 mg·kg-1、50 mg·kg-1、100 mg·kg-1、200 mg·kg-1和500 mg·kg-1, 并以去离子水做空白对照; 复合试验设置2个铜浓度(低铜浓度25 mg·kg-1和高铜浓度200 mg·kg-1)分别与5个草甘膦浓度(0、25 mg·kg-1、50 mg·kg-1、100 mg·kg-1和200 mg·kg-1)复合; 每个处理3次重复, 试验期为35 d。研究了铜和草甘膦的单一及复合施用对蚯蚓的亚急性毒性效应。单一毒性试验结果表明, 蚯蚓对低浓度铜的响应不敏感, 而较高浓度铜使蚯蚓生物量的相对增长率受到显著抑制(α=0.01, r2=0.570), 且未出现死亡, 并且随着铜浓度的增加蚯蚓体内铜含量显著增加(α=0.01, r2=0.905)。与对照相比草甘膦的添加对蚯蚓的生长无显著影响。复合毒性试验结果表明, 草甘膦和铜复合可以降低蚯蚓对铜的吸收, 特别是当铜浓度较高时即200 mg·kg-1, 草甘膦和铜复合可显著降低蚯蚓对铜的吸收, 并且草甘膦能够减轻铜对蚯蚓生物量相对增长率的抑制, 但差异并不显著。以上结果表明, 铜比草甘膦的毒性大很多, 铜与草甘膦复合能够减少蚯蚓对铜的吸收, 缓解铜的毒性。因此本研究认为, 在草甘膦和重金属共存的污染土壤中, 草甘膦能够控制重金属的生物有效性和毒性。Abstract: Interactions of pollutions are among current research focus in environmental sciences. Fungicides contained copper (Cu) and herbicide glyphosate (GPS) are widely used in orchards and other agricultural ecosystems. Co-existence of Cu and GPS could result in combined pollution of soil environment. GPS affects metal behaviors in water and soil systems because its functional groups such as amine, carboxylate and phosphonate react with metal ions to form metal complexes. A laboratory experiment was therefore conducted to investigate the interactions of GPS and Cu with respect to sub-acute toxicity to soil invertebrate earthworms. Earthworms were exposed to spiked soil (70% garden mould and 30% dairy manure) for 35 d with different concentrations of Cu and GPS (technical-grade glyphosate acid). Deionized water was the blank control, Cu concentrations were 25 mg·kg-1, 50 mg·kg-1, 100 mg·kg-1, 200 mg·kg-1 and 400 mg·kg-1 and GPS concentrations were 25 mg·kg-1, 25 mg·kg-1, 100 mg·kg-1, 200 mg·kg-1 and 500 mg·kg-1 by soil dry weight in a single toxicity test. Simultaneously, two Cu levels of 25 mg·kg-1 and 200 mg·kg-1 were mixed by adding 0 mg·kg-1, 25 mg·kg-1, 50 mg·kg-1, 100 mg·kg-1 and 200 mg·kg-1 of GPS in a complementary test. The purpose of the study was to address the possible inductions of earthworm (Eisenia fetida) exposure to single Cu and GPS and the corresponding interactions. The relative growth rate of earthworm biomass and Cu uptake were then measured. Results showed that the relative growth rate of earthworm biomass was significantly inhibited by high Cu concentration (α=0.01, r2=0.570). Furthermore, earthworm Cu content significantly increased with increasing soil Cu concentration (α=0.01, r2 =0.905). GPS had no significant effect on the relative growth rate of earthworm biomass. The complementation test data showed that GPS significantly decreased earthworm Cu burden when soil Cu concentration was 200 mg·kg-1. Higher acute toxicity was noted for Cu than for GPS. To a certain degree, GPS decreased toxicity. Thus GPS was recommended in controlling soil toxicity and bioavailability of soil heavy metals in conditions where both GPS and heavy metals co-exist.