Estimation of the toxicity of sulfadiazine to Daphnia magna using negligible depletion hollow-fiber liquid-phase microextraction independent of ambient pH

Kailin Liu,Min Liu,Xiaomao Zhou,Kun Luo,Shiji Xu,Minghuan Zhang,Lianyang Bai,Lifeng Hu,Yahong Kou,Xiangying Liu

doi:10.1038/srep39798

Abstract

The toxicity of ionizable organic compounds to organisms depends on the pH, which therefore affects risk assessments of these compounds. However, there is not a direct chemical method to predict the toxicity of ionizable organic compounds. To determine whether hollow-fiber liquid-phase microextraction (HF-LPME) is applicable for this purpose, a three-phase HF-LPME was used to measure sulfadiazine and estimate its toxicity to Daphnia magna in solutions of different pH. The result indicated that the sulfadiazine concentrations measured by HF-LPME decreased with increasing pH, which is consistent with the decreased toxicity. The concentration immobilize 50% of the daphnids (EC50) in 48 h calculated from nominal concentrations increased from 11.93 to 273.5 mg L−1 as the pH increased from 6.0 to 8.5, and the coefficient of variation (CV) of the EC50 values reached 104.6%. When calculated from the concentrations measured by HF-LPME (pH 12 acceptor phase), the EC50 ranged from 223.4 to 394.6 mg L−1, and the CV decreased to 27.60%, suggesting that the concentrations measured by HF-LPME can be used to estimate the toxicity of sulfadiazine irrespective of the solution pH.

Highlights

The toxicity of ionizable organic compounds to organisms depends on the pH, which affects risk assessments of these compounds
The toxicity of sulfadiazine to D. magna decreased with increasing pH, the EC50 significantly increased with the pH, with values of 11.93, 97.28 and 273.51 mg L−1 at pH 6.0, 7.5 and 8.5, respectively (Table 1)
Previous toxicity studies using standard procedures indicated that the EC50 values (48 h) of sulfadiazine to for D. magna were 212–221 mg L−1 18,19, which is between the values at pH 7.5 and pH 8.5; our results were consistent with previous results reported by Anskjær, et al.[5], with only the 48-h EC50 at pH 6.0 being slightly lower than the minimum limit (13.4 mg L−1)

Summary

Introduction

The toxicity of ionizable organic compounds to organisms depends on the pH, which affects risk assessments of these compounds. Used to calculate the toxicity, risk assessment could be improved irrespective of the environmental pH14 This determination is time-consuming and not suitable for risk assessment; optimizing a biomimetic method, such as three-phase hollow-fiber liquid-phase microextraction (HF-LPME), to estimate toxicity is important. In this method, the analytes of interest in aqueous samples pass through a thin layer (several microliters) of organic solvent immobilized within the pores of a porous hollow fiber and pass into an acceptor solution inside the lumen of the hollow fiber[15]. The objective of the present study was to use three-phase HF-LPME to measure sulfadiazine concentrations and estimate its toxicity and bioconcentration in D. magna in test solutions of different pH

Objectives

Methods

Results

Conclusion