Abstract
Freshwater green algae Chlorella vulgaris was selected as an adsorbent, and a simple, rapid, economical and environmentally friendly method for the detection of heavy metal Cd in water samples based on preconcentration with C. vulgaris combined with energy dispersive X-ray fluorescence (EDXRF) spectrometry was proposed. Chlorella vulgaris could directly and rapidly adsorb Cd2+ without any pretreatment, and the maximum adsorption efficiency could be obtained when the contact time was 1 min with an optimal pH of 10. The obtained Cd-enriched thin samples after preconcentration with C. vulgaris by suction filtration of reaction solution had very good uniformity, which could be directly measured by EDXRF spectrometry, and the net integral fluorescence intensity of Cd Kα characteristic peak had a very good linear relationship with the initial concentration of Cd in the range of 0.703–74.957 µg ml−1 with a correlation coefficient of 0.9979. When the Cd thin samples with a Cd-enriched region of 15.1 mm in diameter were formed by the developed preconcentration method with suction filtration of 10 ml reaction solution, the detection limit of this method was 0.0654 µg ml−1, which was lower than the maximum allowable discharge concentration of Cd in various industrial wastewaters. The proposed method was simple to operate, and could effectively remove the influence of matrix effect of water samples and effectively improve the sensitivity and stability of EDXRF spectrometry directly detecting heavy metals in water samples, which was successfully applied to detect Cd in real water samples with satisfactory results, and the recoveries ranged from 94.80% to 116.94%. Moreover, this method can be applied to the rapid detection and early warning of excessive Cd in discharged industrial wastewaters. This work will provide a methodological basis for the development of rapid and online monitoring technology and instrument of heavy metal pollutants in water.
Highlights
Wastewaters discharged from various industrial processes such as plating, mining, smelting, dyeing, battery, chemical industry and sewage discharged from agricultural activities usually contain large amounts of heavy metals, including cadmium (Cd)
According to the 3σ/k IUPAC criteria (σ is the standard deviation of multiple measurements for blank sample; k is the slope of linear calibration plot), for the formed Cd thin samples with a Cd-enriched region of 15.1 mm in diameter obtained by the developed preconcentration method with suction filtration of 10 ml reaction solution, the detection limit of this proposed energy dispersive X-ray fluorescence (EDXRF) detection method was 0.0654 μg ml−1, which was lower than the maximum allowable discharge concentration of Cd specified in discharge standards of water pollutants for various industries of China
For the spiked water samples, all the relative standard deviation (RSD) values of 13 the three repeated measurements were no more than 5.05%. These results indicate that the developed method by the combination of preconcentration with C. vulgaris and EDXRF spectrometry could be well applied to the detection of Cd in real water
Summary
Wastewaters discharged from various industrial processes such as plating, mining, smelting, dyeing, battery, chemical industry and sewage discharged from agricultural activities usually contain large amounts of heavy metals, including cadmium (Cd). Cd is one of the most toxic heavy metal environmental pollutants. Due to its characteristics of non-biodegradation, bioaccumulation and concealing, Cd is potentially dangerous for human beings, animals and plants. Once it enters the human body through the food chain, the haematopoiesis, nerves, liver, kidneys, respiratory system, cardiovascular system and reproductive system of human body will be seriously affected [1], which will cause acute and chronic diseases and seriously endanger human health and safety. The rapid, real-time and online detection of Cd in water has very important practical significance for preventing water pollution from heavy metals and protecting the safety of human beings and ecological environment
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