Abstract
The extensive use of glyphosate (N-(phosphonomethyl) glycine) herbicide in agriculture is accompanied by the risk of environmental contamination of aquatic ecosystems. In this study, the effects of glyphosate at different concentrations (50–500 µg ml-1) on three Chlorella species including Chlorella ellipsoidea, Chlorella sorokiniana and Chlorella vulgaris especially in relation to the biomass, pigment contents and photosynthetic efficiency were assessed. After treatment for 24 hr, the acute toxicity results showed that C. vulgaris (IC50 = 449.34 ± 6.20 µg ml-1) was more tolerant to glyphosate than C. ellipsoidea (IC50 = 288.23 ± 23.53 µg ml-1) and C. sorokiniana (IC50 = 174.28 ± 0.50 µg ml-1). After a 72-hr chronic toxicity treatment with glyphosate, glyphosate concentrations decreased to 400–500 µg ml-1 in C. ellipsoidea, 200–300 µg ml-1 in C. sorokiniana and 200–500 µg ml-1 in C. vulgaris respectively. During 24-hr acute toxicity exposure to glyphosate, the pigment contents and maximum quantum efficiency of photosystem II (Fv/Fm) decreased as the concentration of glyphosate increased. Overall, the biomass, pigment contents and photosynthetic efficiency presented a high positive correlation. It is worthwhile to mention that our study provides detailed information on the toxicity and sensitivity of these Chlorella species to glyphosate.
Highlights
Herbicides are commonly used in agricultural systems on a global scale to control weeds and to increase crop yield and quality
After treatment for 24 hr, the acute toxicity results showed that C. vulgaris (IC50 = 449.34 ± 6.20 μg ml-1) was more tolerant to glyphosate than C. ellipsoidea (IC50 = 288.23 ± 23.53 μg ml-1) and C. sorokiniana (IC50 = 174.28 ± 0.50 μg ml-1)
In order to assess the toxic stress of herbicides, this study examined the evolution of the toxic impact of glyphosate on the biomass, pigment contents and photosynthetic efficiency in representative of Chlorella sp. including C. ellipsoidea, C. sorokiniana and C. vulgaris
Summary
Herbicides are commonly used in agricultural systems on a global scale to control weeds and to increase crop yield and quality. Due to improper application practices and excessive use, the lack of control and unbalanced usage of herbicides largely impact environment and lead to detrimental effects on human health and ecosystems, especially in aquatic environments [1]. Microalgae communities serve as an indicators help to evaluate the effects of both chemical and physical environmental parameters on ecosystems [2]. In the case of microalgae, herbicides have the potential to disrupt the balance of the whole ecosystem [3,4,5]. Herbicides have shown to seriously limit impact the biodiversity and limit the number of organisms in microalga ecological systems [6]. Microalgae are primary producers, base link of the aquatic food chain, and respond to environment and chemicals in aquatic ecosystems, their sensitivity to herbicides is critical [7, 8]. Much research supports that microalgae might be the most promising early-alert indicator of changes in the ecological system caused by chemicals [9,10,11]
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