The Odiel and Tinto rivers show singular characteristics due to the significant acid mine drainage (AMD) generated in the first section of their basins and the phosphogypsum (PG) stacks located on their common estuary. AMD leads to low pH and high redox potential, which keep high amounts of toxic elements and radionuclides in dissolution. The objective of this work was to analyse the seasonal evolution of U-Th isotopes and ²¹⁰Po in these rivers and the estuarine mixing zone. Four sampling points were selected (a fluvial point and an estuarine one for each river) and water samples were collected monthly throughout a year. The concentrations of natural radionuclides in the dissolved and particulate phases were determined by alpha spectrometry. The Odiel and Tinto rivers show concentrations of U-Th isotopes and ²¹⁰Po from one to three orders of magnitude higher than background continental waters due to the strong effect of AMD, and ²³⁴U/²³⁸U activity ratios up to 2.

The studied radionuclides show a clear seasonal behaviour in these rivers, with three different stages during the year: (1) concentration peaks observed during November and December due to the “washing effect” produced by the first rainfalls of the hydrological year, (2) a “dilution effect” by runoff in the rainy winter, and (3) a progressive “concentration effect” during the spring and summer. A non-conservative behaviour of the analysed radionuclides in the estuaries was demonstrated due to precipitation processes produced by the increase of pH. The polluted outflows from the PG stacks located in the Tinto estuary produce a significant radioactive impact, mainly during the rainiest months, increasing the concentration of U-isotopes and ²¹⁰Po in the particulate phase.

奥迪尔河和廷托河显示出奇特的特征，这是由于在其盆地的第一部分产生了显着的酸性矿井排水（AMD），并且在其共同河口处形成了磷石膏（PG）烟囱。AMD导致pH值低和氧化还原电势高，从而使大量有毒元素和放射性核素保持溶解状态。这项工作的目的是分析这些河流和河口混合区中U-Th同位素和²¹⁰ Po的季节演变。选择了四个采样点（每个河流有一个河口和一个河口），并在一年中每月收集一次水样。通过α光谱法测定溶解相和颗粒相中天然放射性核素的浓度。奥迪尔河和廷托河显示U-Th同位素的浓度和由于AMD的强大影响，²¹⁰ Po比背景大陆水高出1到3个数量级，并且高达2的²³⁴ U / ²³⁸ U活度比。

所研究的放射性核素在这些河流中表现出明显的季节性行为，在一年中分为三个不同阶段：（1）由于水文学年的第一场降雨产生的“冲洗效应”，在11月和12月观察到了浓度峰值，（2）在多雨的冬季，径流产生“稀释效应”，而在春季和夏季，则产生逐步的“集中效应”。由于pH升高产生的沉淀过程，表明了河口中分析的放射性核素的非保守行为。位于Tinto河口的PG烟囱的污染流出物产生了重大的放射性影响，主要是在最雨的月份，这增加了颗粒相中U同位素和²¹⁰ Po的浓度。