The giant otter, Pteronura brasiliensis, (Zimmermann, 1780), is a semiaquatic carnivore that feeds mainly on fish. Mercury has high toxicity and high potential for bioaccumulation in tissues and biomagnification in organisms through food chains. Thus, as a top predator in the trophic chain, the giant otter has the potential to accumulate mercury by biomagnification. The objective of the present study was to measure the total mercury concentration in giant otter fur samples from an area in the southern Brazilian Pantanal. Fur samples from 19 otters from different social groups were collected from captured animals or were sampled with biopsy darts. Total mercury determination was performed by cold steam spectrophotometry. Mercury concentrations found in the giant otter fur were 7.15 ± 3.41 μg·g^-1 (2.01 to 12.06 μg·g^-1) dry weight. The values are above to the upper limit found in fur samples of otter species not exposed to contamination sources, which typically range from 1 to 5 μg·g^-1. The concentrations found in the study area indicate that even in the southern Pantanal, which is approximately 475 km from gold mining activity, mercury can be considered a threat for giant otters, as well as for riverside populations. It is also important to consider that other anthropogenic sources of mercury, such as pesticides used in agriculture, could affect this population.

巨型水獭（Pimmeronura brasiliensis）（Zimmermann，1780）是一种半水生食肉动物，主要以鱼为食。汞具有高毒性，并具有通过食物链在组织中进行生物富集和在生物体内进行生物放大的潜力。因此，作为营养链中的顶级捕食者，巨型水獭具有通过生物放大作用积聚汞的潜力。本研究的目的是测量来自巴西潘塔纳尔南部地区的大型水獭毛皮样品中的总汞浓度。从捕获的动物中收集来自不同社会群体的19只水獭的皮毛样本，或用活检飞镖采样。总汞的测定通过冷蒸汽分光光度法进行。在巨型水獭皮中发现的汞浓度为7.15±3.41μg·g ^-1（2.01至12.06μg·g ^-1）干重。该值高于未暴露于污染源的水獭物种的毛皮样品中的上限，通常为1至5μg·g ^-1。在研究区域中发现的浓度表明，即使在距金矿开采活动约475公里的潘塔纳尔湿地南部，也可以将汞视为巨型水獭和河沿种群的威胁。还必须考虑到其他人为汞源，例如农业中使用的农药，可能会影响这一人口。