The Toxicity And Ecological Risk Shreshold Of Typical Antibiotics On Aquatic Organisms

Antibiotics have been widely produced and used in the world since they play a significant antibacterial role in their natural,semi-sythetic,and synthetic forms.The clinical and veterinary antibiotics were excreted via urine and feces,and released into the aquatic environment via runoff and permeation of the effluent from municipal wastewater treatment plant and livestock and poultry farming wastewater treatment unit,which may cause the toxic effects on aquatic organisms.A large amount of antibiotics have been detected in the natural environment due to their stability characteristics.The four groups of antibiotics,including sulfonamides,chloramphenicols,quinolones and tetracyclines,occurred frequently in the aqueous environment in China.Therefore,the most commonly detected chloramphenicol(CHL),sulfamethoxazole(SMX),tetracycline(TC)and enrofloxacin(ENR)were selected as model antibiotics.The phytoplankton(i.e.,Pseudokirchneriella szubcapitata),zooplankton(i.e,Daphnia magna),fish(i.e,Danio rerio,and Gobiocypris rarus),and benthic larvae(i.e.,Bellamya quadrata)were selected as the aquatic organisms.This study investigated the acute and chronic toxic effects of typical antibiotics on aquatic organisms,and derived the ecological risk threshold(namely predicted no effect concentration(PNEC))via the species sensitivity distribution(SSD)and the assessment factor(AF).The following conclusions have been drawn as:(1)In the acute toxicity test,the 72 h-median effective concentration(EC50)of CHL,SMX,TC and ENR to Pseudokirchneriella subcapitata were 49.203,1 5.681,1.3 16 and 0.952 mg·L-',respectively,and the confidence limits(95%probability)were 28.033-96.669,12.350-24.469,0.788-3.096 and 0.676-1.692 mg·L-1,respectively.The 48 h-EC50 of CHL,SMX,TC and ENR to Daphnia magna were 129.560,175.780,91.155 and 78.380 mg-L"1,respectively,and the confidence limits(95%probability)were 124.378-148.077161.586-483.408,85.655-97.242 and 55.741-120.384 mg·L"1,respectively.The 96 h-median lethal concentration(LC;50)of CHL and SMX to Danio rerio were>1000 and>600 mg·L-1,and the 96 h-LCso of CHL and SMX to Gobiocypris rarus were>1000 and>600 mg-L-1.The 96 h-LC50 of TC and ENR to Danio rerio were 289.560 and 105.560 mg·L-1,and the confidence limits(95%probability)were 244.610-299.800 and 98.100-114.830 mg·L-1.The 96 h-LC:50 of TC and ENR to Gobiocypris rarus were 144.370 and 146.990 mg·L-1?and the confidence limits(95%probability)were 128.630-149.600 and 132.330-164.950 mg-L-1.The 96 h-LC50 of SMX to Bellamya quadrata was>600 mg·L-1.The 96 h-LC50 of CHL,TC and ENR to Bellamya quadrata were 375.285,226.458 and 279.491 mg·L-1,respectively,and the confidence limits(95%probability)were 272.488-607.853,154.545-299.446 and 205.211-402.083 mg·L-1,,respectively.CHL,SMX.,TC and ENR were moderately,moderately,highly,and extremely toxic to P.seudo kirchneriella subcapitata,and low,low,low,and moderately toxic to Daphnia magna,and low toxic to Danio rerio,Gobiocypris rarus and Bellamya quadrata.(2)The chronic toxicity test showed that four antibiotics inhibited the reproduction of Daphnia magna at varied levels.The 21 d-ECso,the lowest observed effect concentration(LOEC),and the no observed effect concentration(NOEC)of CHL to Daphnia magna were 15.590,2.500 and 1.250 mg-L-1,respectively.The LOEC of SMX,TC and ENR to Daphnia magna were 10.000,14.144 and 10.000 mg·L-1,respectively,and the NOEC of SMX,TC and ENR to Daphnia magna were 3.200,7.072 and 5.000 mg-L-1?respectively.Four antibiotics had no significant effect on the juvenile growth of Gobiocypris rarus.(3)In the flow-through fish test,the activity of superoxide dismutase(SOD)exposed under high ENR concentrations(i.e.,2.5,5,10 mg·L-1)within 28 days was inhibited first and thcen activated.There was a good linear correlation between SOD activity and malonic dialcdehyde(MDA)content,while no obvious trend for catalase(CAT).(4)The PNEC values of four typical antibiotics on freshwater aquatic organisms showed a decreasing order of CHL(138.820[?g·L-1)>TC(120.370(?g·L-1)>SMX(75.810 ?g-L-1)>ENR(63.120]?g·L-1)for short-term exposure test,and ENR(6.709?g·L-1)>CHL(1.190?g-L-1)>SMX(0.944?g-L1)>TC(0.758 ?g·L-1)for long-term exposure test.TC had the highest risk of chronic poisoning,demonstrating that the invetigation of its chronic toxic effect is particularly worthy of attention.