Data on metal accumulation in the tails of the lizard Microlophus atacamensis in a coastal zone of the Atacama Desert, northern Chile: A non-destructive biomonitoring tool for heavy metal pollution

Graphical abstract Image, graphical abstract


a b s t r a c t
In this data article, we investigated the accumulation of heavy metals in the lizard Microlophus atacamensis , in three coastal areas of the Atacama Desert, northern Chile. We captured lizards in a non-intervened area (Parque Nacional Pan de Azucar, PAZ), an area of mining impact (Caleta Palitos, PAL) and an active industrial zone (Puerto de Caldera, CAL). Our methods included a non-lethal sampling of lizard's tails obtained by autotomy. The concentrations of lead, copper, nickel, zinc and cadmium were measured in both soil and prey and compared to those recorded in the lizards' tails. We estimated metal concentrations in the soil, in putative prey and M. atacamensis tails, using atomic absorption spectrophotometry. In order to characterize the trophic ecology of M. atacamensis and to relate it to possible differences in metal loads between sites, we included a few slaughtered animals to perform a stomach contents analysis (SCA). The software R Core Team (2019) was used to carry out all statistical tests to evaluate and analyze the data, applying a priori and a posteriori statistical tests to test the variance and mean hypotheses. Analysis of the data of the content of heavy metals in the tails, prey and soil inhabited by M. atacamensis in PAZ, PAL and CAL showed that the concentration of metals found in the tails and the range of environmental exposure to heavy metals of these animals were related. This article shows for the first time a quantification of the metal concentration on lizard tissues with a non-lethal technique in anthropically disturbed sites in the South Pacific.
© 2020 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license.

Description of data collection
A total of 28 soil, 29 putative preys and 73 tail samples were collected from areas with different degrees of anthropogenic intervention. To leave no doubt that there was no contamination from the used instruments in the sampling process, we have used non-metal instruments. The locations were registered using GPS and the map is provided. Soil samples were collected at a depth of 10-20 cm, the putative preys were obtained manually as well as the tails of lizards.
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Value of the Data
• Knowledge of metals present in the soil, putative preys and lizard tails provides an essential tool for distinguishing between the contribution of these metals from natural sources and the impact of anthropogenic sources from the coastal desert of Atacama (Northern Chile). • The data presented will allow an interdisciplinary interpretation of the environmental damage caused by anthropogenic processes. • The data are unique, but reproducible to the same sites studied or it can be used as a framework for other anthropically disturbed areas. • These data can be used as a supportive tool for decision makers in regulatory bodies related to industrial fields and it can be used to examine any dynamics or changes in the future. • The data shows quantification of the degrees of contamination using a non-destructive or non-lethal technique.

Data description
The Atacama Desert, in Northern Chile, is one of the oldest deserts of the planet and has been arid to semi-arid for millions of years. It is one of the richest territories in the world in terms of porphyry copper deposits, whose heavy mining industry generates waste that significantly affects environmental sustainability.
In this article, we present collected data from January 2017 to November 2018 from three sites, a coastal cove with a well-known legacy of mine tailing discharge (Caleta Palitos, PAL), an active industrial city port (Caldera, CAL) and a National Park (Pan de Azucar, PAZ), spanning about 130 km of a coastal transect of the Atacama Desert ( Table 1 ).
Soil: We obtained a total of 28 samples to determine the metal content in soils of the studied sites. The samples were stored in plastic bags previously treated with HCl (1M). Considering the same sampling transect line lizards were also captured ( Fig. 1 ).
Prey: 29 putative preys were obtained manually at the three sites using hand searches and, where necessary (e.g. for flying insects), using hand nets. Samples were returned to the laboratory, identified, and where necessary soft tissues were removed from inorganic carapaces (decapods) or shells (mollusks). Samples were then dried (60 °C for 48 h) before processing for subsequent analysis for metal concentrations.
Tails: A total of 72 adult M. atacamensis lizards (CAL n = 20, PAL n = 22, PAZ n = 30) ( Table 1 ) were captured randomly within five meters of each side of an imaginary transect during the hottest hours of the day (11:0 0-15:0 0 h) [2] . We captured each animal carefully using a rod with a sliding lasso in order to preserve their original tails, ensuring that the process of autotomy had not taken place [3] .
Subsequently, in the laboratory the collected individuals were sexed, measured and weighed [ 4 , 5 ]. All individuals demonstrated autotomy of their tails; thus, there was no need to remove   them surgically. After sacrificing 27 lizards, their soft parts (stomach, lungs, liver, heart and kidney) were dissected out. Finally, after measuring tissues weight, we stored the tails and soft tissues in sterile vials for subsequent processing and analysis for heavy metals.

Experimental design, materials, and methods
Stomach content: Twenty-seven M. atacamensis from the three sites studied (CAL n = 10, PAZ n = 10, PAL n = 7) were dissected. The stomach content samples were returned to the laboratory, identified, and when necessary, soft tissues were removed from inorganic carapaces (decapods), shells (mollusks) or flowers. The stomach contents were observed under a dissection microscope and identified to the highest possible taxonomic resolution supported by a series of keys and identification guides [6][7][8][9] . The total blotted wet mass of each prey category was estimated to ± 0.001 g. We determined the relative importance of each prey to the diet of M. atacamensis by calculating the frequency of occurrence (FO) and the percentage contribution by mass (%M) [10] ( Table 2 ).
Heavy metals (Lead, Copper, Nickel, Zinc and Cadmium): For the quantification of metals per site the methodology described by Castillo and Valdés [11] was followed for the analytical pretreatment on putative preys and tails ( Table 1 ). The content of metals in soil was measured in the fraction < 63 μm, after drying the samples at 40 °C. For this, between 0.2 and 0.6 g of dry soil was disaggregated in a MARS-X microwave digester (CEM model 350) with a mixture 12 ml of HNO3:HCl (3: 1 ratio) at 150 °C for 20 min according to the US-EPA 3051A procedure (EPA, 2007). Finally, the resulting solution was filtered with a 0.45 μm filter and diluted to 25 ml with deionized water [12] .
The soft tissues were separated and homogenized in an agate mortar for biological material until a wet paste was obtained. Subsequently, between 0.5 and 1.0 g of sample was added in a Teflon beaker with 10 ml of HNO 3 (Suprapur, Merck®) and was disintegrated into a microwave digester (MARS-5), according to the US-EPA procedure 3051A (digestion at 180 °C for 10 minutes). Finally, the resulting solution was diluted to 25 ml with deionized water.
The analysis of Pb, Cu, Ni, Zn and Cd from organisms and soil was performed with an atomic absorption spectrophotometer (Shimadzu AA-6300) by flame technique. The analytical procedure was checked using the certified standard reference material DORM-3 and MESS-3 (National Research Council, Canada). The analytical error was less than 5% and the results were expressed as mg kg -1 ( Table 3 ).

Calculation of the Bioaccumulation Factor (BAF), Potential Ecological Risk (RI), and Trophic Transfer Factor (TTF):
The BAF was calculated dividing the metal concentration detected in the lizard tails ( C biota , mg kg −1 ) by the concentration of the metal measured in the sediment ( C soil , mg kg −1 , Table 4 ).
The RI of total heavy metals toxicity was calculated using Eq. (1) [13] .
In Eq. (1) , where T r is the toxic response factor for a specific heavy metal, this factor was 30, 5, 5, 5, and 1 for Cd, Cu, Ni, Pb, and Zn respectively. C i is the metal concentration in the samples, C r is the background value of heavy metal in soil ( Table 5 ) [14] , E r is the individual potential ecological risk factor, RI is a composite index that indicates the potential ecological risk of total heavy metals in soils, and n is the total number of the estimated heavy metals ( Table 6 ).
Calculation of Trophic Transfer Factor (TTF): It is calculated dividing the metal concentration in the organism's tissue by the metal concentration in the organism's food [15] . A TTF value > 1 indicates a possibility of biomagnification, while values < 1 suggest that biomagnification is unlikely. For the TTF calculations, we considered a range of assimilation efficiencies and ingestion rates for all organisms ( Table 7 ). Rearranging this equation to express the ratio of metal concentration in an organism to the concentration in its prey allows an assessment of the potential of a particular metal to biomagnify at different sequential steps in the food chain.

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.
where T r is the toxic response factor for a specific heavy metal, this factor was 30, 5, 5, 5, and 1 for Cd, Cu, Ni, Pb, and Zn, respectively. C i is the metal concentration, C r is the background value of heavy metal in soil E r is the individual potential ecological risk factor RI is a composite index that indicates the potential ecological risk of total heavy metals in soils, and n is the total number of the estimated heavy metals RI < 150 Low Risk 150 < RI < 300 Moderate Risk 30 0 < RI < 60 0 Considerable Risk RI > 600 High Risk Table 4 . BAF of metals in the three sites studied. Values greater than 1 imply that there is bioaccumulation with respect to the reference environmental matrix. Bioaccumulation factors ( C biota , mg kg −1 )/( C soil , mg kg −1 ) higher than 1 are shown in bold.

Ethics statement
We confirm that the data presented in this report comply with the ARRIVE guidelines and was carried out with the approval of the Ethics Committee of the University of Antofagasta, Chile. Also, animal capture was authorized by the local competent authority, the Chilean Agricultural and Livestock Service.

Supplementary materials
Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.dib.2020.106032 .