Acetylcholinesterase activity in the freshwater shrimp Caridina nilotica as a biomarker of Roundup? herbicide pollution of freshwater systems in South Africa

摘要

The use of Caridina nilotica whole-body acetylcholinesterase (AChE) activity as a potential biomarker of Roundup? pollution of aquatic ecosystems was investigated. Forty days post hatch (dph) shrimps were exposed to different concentrations of 0.0, 4.3, 6.7, 10.5, 16.4, 25.6 and 40.0 mg/L in a 96 h acute toxicity test; and 0.0, 2.2, 2.8, 3.4, 4.3 and 5.4 mg/L in a 21 d chronic toxicity test. Whole-body AChE activities were determined at the end of the exposure periods by spectrophotometric assay of sample extract; activities were then normalized against protein contents in the samples and expressed in nanomoles of substrate hydrolyzed. Results of both tests showed that AChE activity was concentration-dependent. Mean AChE activities and standard deviations (±SD) for 96 h acute toxicity were 3.6239 (±0.4185), 3.4157 (±1.1842), 2.537 (±1.3989), 2.4253 (± 1.4202), 2.4127 (±1.9097), 2.0017 (± 1.1080) and 2.316 (±0.4001) nmol/min/mg protein; while activity levels for 21 d test were 3.6907(±0.3401), 2.8473 (±0.713), 2.9134 (± 0.9879), 2.6738 (±0.7117), 2.3019 (±0.4464) and 2.1478 (±0.864) nmol/min/mg protein. Reference basal AChE activity for 40 dph C. nilotica based on the two control groups was estimated as 3.6907 (±0.3401) nmol/min/mg proteins. The present work provides ecotoxicological basis for the possible use of AChE activity in C. nilotica as a biomarker for monitoring Roundup? pollution in freshwater systems.