The estuary of Río de la Plata, in the eastern coast of South America, is a highly anthropized area that brings a high load of contaminants to the surrounding waters which may have detrimental effects on the local marine fauna. The franciscana dolphin (Pontoporia blainvillei) is a small cetacean species endemic of the southwestern Atlantic Ocean listed as Vulnerable in the IUCN red list. In this study, we assessed the concentrations of 13 trace elements in bone samples from 100 franciscana dolphins that were found stranded dead or incidentally bycaught in the Río de la Plata and adjacent coast between 1953 and 2015. Elements were, in decreasing order of mean concentrations: Zn > Sr > Fe > Al > Mn > Cu > Pb > Cr > Ni > As > Hg > Cd > Se. The concentrations of Al, Cr and Fe were slightly higher in females than in males. The concentrations of As, Ni, and Pb significantly decreased with body length. Throughout the study period, the concentrations of Al, Cr, Cu, Fe, Mn and Ni significantly increased, while the concentrations of As, Pb and Sr significantly decreased. The increasing trends may be due to increased inputs from river discharges, the leather industry and petroleum refineries, while the decrease in Pb may be due to the ban in the use of this element as an additive in gasoline and as component of car batteries. This investigation supports the validity of analysing trace element analyses in bone, a tissue available in scientific collections and museums, to retrospectively examine variation over long temporal scales and thus assess long-term trends in pollution.

南美东部海岸的里奥·德拉普拉塔河口是一个高度人为化的地区，给周围水域带来了大量污染物，可能会对当地海洋动物群造成不利影响。方济各会的海豚（Pontoporia blainvillei）是西南大西洋的一种小型鲸类物种特有种，在世界自然保护联盟（IUCN）的红色名录中被列为易危物种。在这项研究中，我们评估了1953年至2015年之间在里约热内卢和附近海岸被困死或偶然捕获的100只方济各会海豚的骨骼样品中13种微量元素的浓度。这些元素的平均浓度降序排列锌>锶>铁>铝>锰>铜>铅>铬>镍>砷>汞>镉>硒 女性的铝，铬和铁的含量略高于男性。砷，镍和铅的浓度随体长而显着降低。在整个研究期间，Al，Cr，Cu，Fe，Mn和Ni的浓度显着增加，而As，Pb和Sr的浓度显着降低。趋势的增加可能是由于河流排放，皮革工业和石油精炼厂的投入增加，而铅的减少可能是由于禁止将该元素用作汽油中的添加剂和用作汽车电池的组成部分。这项研究支持分析骨骼中微量元素分析的有效性，骨骼是科学收藏品和博物馆中可用的组织，可以回顾性地检查长期尺度上的变化，从而评估污染的长期趋势。