Dataset of concentrations of mercury and methylmercury in fish from a tropical river impacted by gold mining in the Colombian Pacific

This data article includes information on the impact of gold mining along five zones of a tropical river in the Pacific region of Colombia. The concentrations of total mercury (THg), total length, mertimercury (MeHg) were determined in 16 species of fish. With this information, it was shown as the concentrations of mercury in fish are influenced by the distribution in the contamination along the Atrato River Basin [1]. Further, THg and MeHg concentrations were related with the trophic level to show biomagnification, and with total length to show bioaccumulation, which is important to establish the potential risk to the environment and also to the health of the inhabitants living along the basin from the consumption of fish.


Value of the Data
• The data set includes valuable MeHg concentrations in fish samples ( n = 520) collected in the Atrato River Basin, a tropical ecosystem highly impacted by goldmining. • The data set contains extremely scarce and therefore very valuable MeHg concentration values in fish, which are more suitable than THg values for human health risk assessment. • The data set describes the distribution of the contamination by mercury in five areas of the Atrato River basin. Also show the correlations between THg (n = 842) and MeHg concentrations and the total length of the fish per area. • The data set can be used as a reference to identify the most polluted areas throughout the basin, establish possible environmental effects and the risk to human health from fish consumption.

Data Description
In this article, we will describe data on mercury concentrations in fish samples of 16 different species, from five areas of the Atrato River Basin, a tropical ecosystem highly impacted by gold mining [1] . The data set was summarized in Tables 1-5 . They describe the THg and MeHg concentrations and length of fish caught in the areas of: Rio Quito (RQ), Medio Atrato (MA), Table 1 Total mercury concentrations (THg), total length, methylmercury concentrations (MeHg) and percentage of methylmercury in fish captured in the Rio Quito (RQ) zone, Atrato River Basin, Colombia. P: piscivore, C: carnivore, OC: omnivore with a tendency to carnivore, O: omnivore, D: detritivore. The RQ site is located in the south-central zone of the Chocó Department, and the fish samples were caught in the Quito River within 5  ( continued on next page )  ( n = 7) for CUT zones. Within of this samples, 4.5% ( n = 7) for RQ, 11.6% ( n = 23) for MA, 37.7% ( n = 61) for MVF, 11.5% ( n = 28) for RS and 2.4% ( n = 2) for CUT, exceeded the WHO maximum limit of THg in fish for human consumption (500 μg/kg −1 w/w) [2] . For samples of fish with non-carnivore habits, the WHO limit of 200 μg/kg −1 w/w) [3] was exceeded in 4.5% ( n = 7) for RQ, and 1.2% ( n = 1) for CUT. Within of this samples, 2.6% ( n = 4) for RQ exceeded the WHO limit 500 μg/kg −1 w/w) [2] . The data also show that methylmercury is the mercury species found in highest queantity among fish samples analyzed (68.1% -98.8%); therefore, the risk of mercury contamination from fish ingestion, especially in the inhabitants of the MVF zone, is high. This data set was useful to describe the Spearman's correlation coefficients between THg and MeHg concentrations and the total length of the fish, with which the bioaccumulation of these Table 2 Total mercury concentrations (THg). total length. methylmercury concentrations (MeHg) and percentage of methylmercury in fish captured in the Medio Atrato (MA) zone, Atrato River Basin. Colombia. P: piscivore, C: carnivore, OC: omnivore with a tendency to carnivore, OPV: omnivore with preference for fish and vegetal material, O: omnivore, D: detritivore. The MA site is located in the south-central zone of the Chocó Department (north of Río Quito zone), and the fish samples were caught in the Atrato River within 5 °52 01 N 76 °42 33 W and 6 °10 13 N 76 °42 56 W.

Species
THg Ageneiosus pardalis (P) 1   ( continued on next page ) pollutants could be established in fish species of each of the studied areas. The data set also served to shown the median concentration of THg and MeHg in fish tissues by species in all the areas studied, and how many analyzed samples surpassed the warning levels for populations at risk and the maximum limits recommended for human consumption of fish established by WHO [ 2 , 3 ]. Finally, in data set, it is shown that MeHg was the predominant form of mercury in the fish of the Atrato River Basin.

Sampling collection
The fish samples were obtained in five areas of the Atrato River Basin, between April and December 2019, subsequently classified using specialized keys [4] . A total of 842 samples were obtained, the length and weight of the fish were measured and a portion of dorsal muscle of 20-50 grams (g) was taken. The samples obtained were stored in polyethylene bags and refrigerated until the measurement of THg and MeHg concentrations.

Analysis of mercury species
To determine THg concentrations, fish samples were lyophilized for several days to dryness, then 0.02 g of sample was taken and introduced into a direct mercury analyzer (DMA-80 TRI-CELL, Milestone Inc., Italy), according the EPA 7473 method [5] . A certified dogfish muscle standard DORM-2 (4.46 ± 0.25 μg g −1 ) from NRCC was used for process quality control. The recovery percentage of THg (99.6 ± 0.2%, n = 3), the detection and quantification limit were calculated based on the methodology proposed by Marrugo-Negrete et al., [6] .
For the measurements of MeHg concentrations, 0.2-0.3 g of fresh fish were used, the samples were subjected to digestion in a 50 mL centrifuge tube, with 10 mL of hydrobromic acid by manual shaking. To this solution 20 mL of toluene was added, then the mixture was stirred vigorously for 2 min (min). Then, the resulting mixture was centrifuged for 10 min at 30 0 0 rpm, subsequently 15 mL of the upper organic phase were extracted, which were added in a 50 mL tubes containing 6.0 mL of 1% L-cysteine solution. Finally, a 100 μL aliquot of the aqueous phase was taken and injected into a direct mercury analyzer [7] .

Ethics Statement
The authors declare that they have read and follow the ethical requirements for publication in Data in Brief.

CRediT Author Statement
Carlos Salazar-Camacho: Writing-Reviewing and Editing. Manuel Salas-Moreno: Performed the experiments, and data/evidence collection. Wrote the initial draft. Roberth Paternina-Uribe : Supervision, visualization of the Investigation. José Marrugo-Negrete: Developed and designed the methodology for investigation, provided reagents, materials, instrumentation and computing resources for direct mercury analyzer, critical review, commentary and revision for the prepublication stage. Sergi Díez: Supervision, revision for the pre-publication stage .

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships which have or could be perceived to have influenced the work reported in this article.
'DLC', to Ministry of Science, Technology and Innovation (MINCIENCIAS/COLCIENCIAS) for financing of the codified project 849-2018. This work was partly funded by the CSIC through the project iCOOP + 2018-COOPB20362 .