Abstract

The presence of coal-based power plants and coal mine in the Waterberg area subjects the Mokolo River to potentially toxic elements (PTEs) such as mercury (Hg). Mercury is an extremely toxic element. Thus, monitoring and chemical speciation of Hg in water bodies; particularly in sediments is a vital tool for assessing water quality. The objective of this study was to investigate the levels of Hg(II) and methyl Hg (MeHg(I)) in sediment samples collected from Mokolo River in different seasons, as well as examining factors such as pH, temperature and organic matter content, which could affect Hg methylation rates. An ultrasonic based method was used for the extraction of Hg species in sediments. This was followed by the chromatographic separation and detection of Hg(II) and MeHg(I) by the on-line coupling of high-performance liquid chromatography (HPLC) to inductively coupled plasma-mass spectrometry (ICP-MS). A solution containing HCl and 2-mercaptoethanol was employed for the extraction of Hg species in sediments. Separation of the two species of Hg was achieved using isocratic elution mode with a mobile phase containing L-cysteine, 2-mercaptoethanol, ammonium acetate and methanol. The accuracy of the method was checked and yielded a percentage recovery of 86%. The Hg(II) concentrations ranged from 38.4 to 89.05 ng g⁻¹ and 34.8 to 57.3 ng g⁻¹ in low and high flow seasons, respectively. The concentrations of MeHg(I) ranged from 0.702 to 4.5 ng g⁻¹ and 0.5 to 2.5 ng g⁻¹ in the low and high flow seasons, respectively. Factors such as pH and temperature were found to influence the methylation rates, however correlation couldn’t be established to organic matter content due to similar amount of organic matter in all the samples.

摘要

沃特伯格地区的煤电厂和煤矿使莫科洛河受到潜在有毒元素 (PTE) 的影响，例如汞 (Hg)。汞是一种剧毒元素。因此，水体中汞的监测和化学形态分析；特别是在沉积物中，它是评估水质的重要工具。本研究的目的是调查不同季节从莫科洛河采集的沉积物样本中 Hg(II) 和甲基 Hg (MeHg(I)) 的含量，并检查 pH、温度和有机物含量等因素，这可能会影响 Hg 甲基化率。基于超声波的方法用于提取沉积物中的汞。随后，通过高效液相色谱 (HPLC) 与电感耦合等离子体质谱 (ICP-MS) 的在线耦合，对 Hg(II) 和 MeHg(I) 进行色谱分离和检测。使用含有 HCl 和 2-巯基乙醇的溶液提取沉积物中的汞。使用含有 L-半胱氨酸、2-巯基乙醇、乙酸铵和甲醇的流动相使用等度洗脱模式实现了两种汞的分离。对该方法的准确度进行了检查，回收率为 86%。Hg(II) 浓度范围为 38.4 至 89.05 ng g 使用含有 L-半胱氨酸、2-巯基乙醇、乙酸铵和甲醇的流动相使用等度洗脱模式实现了两种汞的分离。对该方法的准确度进行了检查，回收率为 86%。Hg(II) 浓度范围为 38.4 至 89.05 ng g 使用含有 L-半胱氨酸、2-巯基乙醇、乙酸铵和甲醇的流动相使用等度洗脱模式实现了两种汞的分离。对该方法的准确度进行了检查，回收率为 86%。Hg(II) 浓度范围为 38.4 至 89.05 ng g^-1和 34.8 至 57.3 ng g ^-1在低流量和高流量季节分别。在低流量和高流量季节，MeHg(I) 的浓度范围分别为 0.702 至 4.5 ng g ^-1和 0.5 至 2.5 ng g ^-1。发现 pH 值和温度等因素会影响甲基化速率，但由于所有样品中的有机物含量相似，因此无法建立与有机物含量的相关性。