Land Use in Habitats Affects Metal Concentrations in Wild Lizards Around a Former Lead Mining Site

ABSTRACT

populations. 10,11 Until remediation is complete, humans and animals continue to be 57 exposed to toxic substances. Moreover, even if the environment is not suitable for people 58 to live in, since contamination sources often correspond with local economic drivers, 59 social communities and economic activities continue to flourish and fuel urbanization 60 regardless. Therefore, appropriate city planning should be conducted before mass 61 construction begins, so that people can receive the benefits of urbanization while their 62 exposure to environmental pollutants is mitigated. 63 Kabwe, in the Republic of Zambia, is a remarkable example of a city undergoing 64 urban expansion in an environment that has long been contaminated. 12 In Kabwe, the 65 primary contamination source is a lead (Pb) and zinc (Zn) mine. After the mine closed in 66 1993, slags were deposited in the open environment on the premises (S14º27′44″, The Pb contamination in Kabwe has been intensively analyzed, due to the high 76 toxicity of Pb and the associated health risk to animals. Pb is a nonessential element and 77 can cause various toxic effects, including neurodevelopmental and cardiovascular 78 disorders, renal failure, and hypochromic anemia. 19 Recent guidelines require exposure 79 to Pb to be minimized as much as possible. 20,21 To achieve this goal, it is necessary to 80 understand the exposure pathways and factors that affect the amount of exposure. themselves to humans and settle in houses. 28 Therefore, this species can be used to 96 monitor a wide range of geographic areas. In addition, its home range is thought to be 97 less than 500 m 2 , 29 which is relatively small compared to its body size, 30 so it can be used 98 to compare the status of locations that are close to each other. This is important, because 99 few other species have such small home ranges. The lizards eat a variety of insects, such 100 as beetles, flies, and grasshoppers. They forage actively but also bask in strategic position 101 so that they can dart forward to catch passing prey. 28 Although they may sometimes 102 accidentally eat soil or small stones, their main source of contaminants via oral exposure 103 is assumed to be the insects they eat. This feature is optimal for identifying exposure 104 sources. Together, these characteristics make T. wahlbergii an ideal species for 105 investigating differences in metal accumulation among individual animals living in 106 different environments.

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The objective of this study is to explore the environmental factors affecting the 108 contamination status of living organisms by comparing metal (Pb, Zn, Cd, Cu, nickel 109 [Ni]) and As concentrations in lizards inhabiting various locations and a range of 110 environments.

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The primary ore mineral assemblage and metal production history in Kabwe are 115 described in SI (Supporting Information) 1.

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The sampling of lizards and soil was conducted in the vicinity of the Kabwe Pb-117 Zn mine from May to September 2017, which corresponded to the dry season in the region 118 (SI2, Figure S1). The distance from the mine to the sampling sites ranged from 0.26 to 119 21.2 km (SI2, Figure S2). The sampling sites were accurately located using global   Table S1. After purification, 144 PCR products were sequenced using the same primers. All nucleotide sequences were 145 confirmed by the Fasmac sequencing service (Kanagawa, Japan). Sequences were aligned 146 and the phylogenetic tree was constructed using MEGA7 software (Molecular 147 Evolutionary Genetics Analysis version 6.0). 31,32 Information on the 12S rRNA genes 148 used in the phylogenic analysis is shown in SI3, Table S2. Tokyo, Japan) and digested in a microwave digestion system (Speed Wave MWS-2, 165 Berghof, Eningen, Germany). Parameters for digestion are shown in SI4, Table S3. 166 Analysis of Pb, Zn, Cd, Cu, Ni, and As content was performed using inductively     Figure S9; SI12, Figure S11) and NDVI 216 annual averages (SI12, Figure S12). previous research, 14,41 which means that soil contamination is still a cause for concern in 237 Kabwe. In contrast, even the maximum concentrations of Ni and As were lower than the 238 Eco-SSL values. As shown in SI10, Figure S8, concentrations of Pb, Zn, Cd, Cu, and As 239 in the soil were negatively correlated with distance from the mine (p < 0.0001). Therefore, 240 the mine can be identified as the primary metal contamination source in Kabwe. For Ni, 241 however, the concentrations in the soil were low, and this was the only element that did

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The strongest correlations were between livers and blood and between lungs and blood 262 (both ρ = 0.91, p < 0.0001). Therefore, it is reasonable to assume that the accumulation  Pb concentration in the lizards inhabiting these areas.

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The pH values of most of the soil samples were close to neutral (median 7.56), 295 as shown in SI8, Figure S7, although one sample exhibited an extremely high pH (11.5). 296 This might have been caused by fire, since high temperatures and ash promote 297 alkalization of soil. 42,43 In fact, controlled burns are commonly used in Kabwe as a way it is reasonable that the high soil pH value would negatively affect liver Pb concentration 300 as shown in Table1.

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The frequency distribution of the angle of the sites between the mine and ESE, 302 14 the prevailing wind direction is shown in SI7, Figure S6. The distribution indicated that 303 64% of all sampling sites were located downwind of the mine (angle from ESE > 90º).

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Although Figure 2 suggests that lizards on the west side of the mine showed higher 305 concentrations of Pb than those living on the east side, there was no significant effect of 306 wind direction (angle from ESE in Table 1).   Table 1.  The median NDVI value was 0.315 and the range was from 0.050 to 0.486 (SI6, 327 Figure S4). To confirm the validity of the link between vegetation status and the land use 328 categories defined in this study, the NDVI value was compared among different land use 329 categories (SI12, Figure S12). The NDVI value increased in the following order; bare 330 fields ≈ residential areas < open fields < green fields (p < 0.05). There was no significant 331 difference between bare fields and residential areas. Since the average annual NDVI was 332 consistent with the land use categories, we attempted to use it as a parameter to describe 333 land use. However, despite the significant differences in the effects of different land use 334 categories on liver Pb concentrations (Table 1 and Figure 3) エラー! 参照元が見つか 335 りません。, the effect of NDVI was not significant (Table 1). This striking difference 336 between the effects of the land use categories used in this study and that of NDVI can be 337 explained by the fact that the calculation of NDVI does not reflect the existence of houses.    In the case of oral exposure, Pb is absorbed from the digestive tract, enters 379 systematic circulation, and is subsequently delivered to every organ, including the lungs.  In rapidly developing countries, land-use patterns are altered and diversified through 400 urbanization. Topsoil is often exposed to wind at construction sites or along temporary 401 roads. Our results suggest that these bare lands produce dust that is contaminated with