Mercury and selenium concentrations in fishes of the Upper Colorado River Basin, southwestern United States: A retrospective assessment

Abstract

Mercury (Hg) and selenium (Se) are contaminants of concern for fish in the Upper Colorado River Basin (UCRB). We explored Hg and Se in fish tissues (2,324 individuals) collected over 50 years from the UCRB. Samples include native and non-native fish collected from lotic waterbodies spanning 7 major tributaries to the Colorado River. There was little variation of total mercury (THg) in fish assemblages basin-wide and only 13% (272/ 1959) of individual fish samples exceeded the fish health benchmark (0.27 μg THg/g ww).Most THg exceedances were observed in the White-Yampa tributary whereas the San Juan had the lowest mean THg concentration. Risks associated with THg are species specific with exceedances dominated by Colorado Pikeminnow (mean = 0.38 and standard error ± 0.08 μg THg/g ww) and Roundtail Chub (0.24 ± 0.06 μg THg/g ww). For Se, 48% (827/1720) of all individuals exceeded the fish health benchmark (5.

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“…With a ratio (SeT/HgT) greater than 1, the antagonistic effect occurs between mercury and selenium, the latter thus protecting aquatic organisms against the toxicity of mercury. Similar results have been found in previous work [14], [23]- [26]. In addition to the three species of fish studied previously, we also measured in parallel the selenium and the mercury in the crabs and molluscs Limnaea sp populating the various rivers because being part of the food habits of the neighboring populations.…”

“…It is a good thing to minimize the risk of mercury contamination. Similar results from high concentrations of selenium relative to mercury in fish have been found in tropical estuaries in southeast Brazil [25], in Turkish waters [23], in the Colorado River basin in the southwest of the United States [14].…”

“…This accumulation occurs either directly by adsorption through the skin and gill membranes during their respiration, or indirectly by ingestion of already contaminated prey [11]- [13]. Despite their benefits for human health, crabs, fish and molluscs can contain varying amounts of potentially toxic substances, especially heavy metals caused by water pollution [14]- [17].…”

“…It is known as an effective agent to detoxify mercury (Hg) and to offer some protection against the toxicity of mercury (Hg) by reducing the accumulation of Hg in mammals and fish. The presence of selenium in the environment and food is considered to be a bioindicator of the harmful effects of [14], [17], [23], [24].…”

Temporal Influences on Selenium Partitioning, Trophic Transfer, and Exposure in a Major U.S. River

“…Based on Se concentrations from October 2015/2016 collections of the caddisfly (mean = 3.90, range = 2.14–5.29 μg g –1 dw) and Roundtail Chub (mean = 6.11, range = 4.94–7.62 μg g –1 dw, Table S7), we predicted that LGRB Razorback Sucker and Colorado Pikeminnow whole-body concentrations ranged from 2.16 to 5.34 and 5.93 to 9.14 μg g –1 dw, respectively, with mean concentrations of 3.94 and 7.33 μg g –1 dw. These predictions are higher than concentrations in fish collected across the upper Colorado River Basin between 1962 and 2011 (3.37 and 4.47 μg g –1 dw for Razorback Sucker and Colorado Pikeminnow, respectively) reported by Day et al in 2020 . Selenium concentrations in almost all Speckled Dace (91%, n = 201/221) and Roundtail Chub (96%, n = 53/55) collected in October 2015/2016 exceeded the broadly accepted whole-body Se toxicity threshold of 4.0 μg g –1 dwa threshold supported by a wide range of field and lab-based exposure studies investigating both sublethal and mortality endpoints .…”