不同粒径轮胎微塑料对大型溞的慢性毒性研究

Chronic Toxicity of Tire-derived Microplastics of Different Sizes to Daphnia magna

轮胎微塑料是环境中微塑料的重要来源之一,而关于环境浓度轮胎微塑料长期暴露的慢性毒性研究相对较少,其毒性机制尚不明晰。本文以大型溞为受试生物,研究不同粒径(依次过100目、150目和200目筛)轮胎微塑料对大型溞的存活、蜕皮和繁殖的影响,并通过测定大型溞体内重金属累积量及蛋白质/脂肪比值变化来分析轮胎微塑料的致毒机制。结果表明,轮胎微塑料暴露组中大型溞的死亡率均<20%,轮胎微塑料对大型溞蜕皮数和平均产幼数均无明显的不利影响,但对存活率的影响与颗粒粒径相关,在0.5 mg·L^(-1)时存活率随粒径的减小而升高,62.5 mg·L^(-1)时则刚好相反。此外,暴露在62.5 mg·L^(-1)轮胎微塑料悬浮液中大型溞初次生产的时间推迟3~5 d,内禀增长率降低,这可能是由轮胎微塑料的摄入所导致的。摄入的轮胎微塑料本身对大型溞肠道造成刺激,并在其体内释放有害物质,这从暴露后大型溞体内重金属Co、Cu和Zn含量的增加可以看出。因此,环境相关浓度下轮胎微塑料的摄入对水生生物(如大型溞)造成的负面影响很小,但道路冲刷雨水的直接受纳水体可能会因为轮胎微塑料的存在而威胁水生生态系统健康。

Tire-derived microplastics(TMPs)are recognized as a major source of microplastic in the environment.However,studies on the toxicity of TMPs are limited,and their associated toxicity mechanism still remains unclear.Thus,we investigated the chronic toxicity effects of the presence of TMPs,by exposing Daphnia magna(D.magna)to TMPs of three different size ranges(by successively sieving through three sieves with a mesh-number of 100,150,and 200 respectively)at two different concentrations(0.5 mg·L^(-1)and 62.5 mg·L^(-1)).The mortality,molting and reproduction of D.magna were selected as toxicity endpoints,and the related toxicity mechanism was discussed based on the change of the metal concentrations and the protein-to-lipid ratios of organism tissue.The toxicity results showed that the 21-d mortality of D.magna at all exposed conditions were less than 20%,and no significant adverse effects on the molting and reproduction.Particularly,larger TMPs were more toxic to D.magna at the lower concentration of TMPs(0.5 mg·L^(-1)),whereas smaller TMPs were more toxic at higher exposure concentration(62.5 mg·L^(-1)).Further,higher concentration of TMPs influenced the reproduction of D.magna by delaying the time of the first brood for 3~5 d.As evidenced by elevated tissue metal concentrations,these toxic effects at the higher concentration TMPs treatment were likely attributed to ingestion of TMPs,which may irritate the physiological activity of guts in the organism and release toxic chemicals to the organism.These findings suggest that long-term exposure to environmentally-realistic levels of TMPs causes no to low level of toxicity to the aquatic organism such as D.magna,yet the health of aquatic ecosystem that receives direct input of road runoff may be influenced by the presence of high concentration of TMPs.