Heavy Metals in Native Potato and Health Risk Assessment in Highland Andean Zones of Junín, Peru

Heavy metals are transferred from the abiotic environment to living organ-isms, accumulate in food, contaminate the food chain, and are an important route of human exposure involving a potential health risk. In this study, the concentrations of heavy metals (Cd, Fe, Pb, Zn and As) in agricultural soils and tubers of Solanum tuberosum spp. andigena (native potato) were eva-luated. Also, an assessment of the health risk associated with the daily intake by the local population was performed in the four districts of the department of Junín, between altitudes of 3800 m to 4200 m. The heavy metals concentrations in soils with native potato cultivation followed the following decreasing order of Fe > Zn > Pb > As > Cd, with values below national standards. The heavy metals content in native potatoes was below the limits recommended by international standards with the exception of Pb. The bioconcentration factor (BCF) for the two native potato varieties in decreasing order was Zn > Cd > Pb > As > Fe, all less than 0.5. The estimated daily intake of metals (EDIM) in adults and children through the consumption of native potatoes was higher for Fe and Zn. The threshold carcinogenic risk values (TCR) for As exceeded the safety limits 1 × 10 −4 . It is concluded that the residents in the four high Andean localities would be exposed to carcinogenic adverse health effects associated with the intake of native potatoes. It is important to moni-tor the concentration of As and other heavy metals in the Andean soils and crops in order to implement a soil and crop management program to ensure food quality.


Introduction
Heavy metals represent a source of contamination and an environmental and human health problem [1]. The soil is the entry point for heavy metals in plants and, consequently, also in the food chain [2]. There are different sources of heavy metals in the soil such as natural sources and anthropogenic sources (mining and industrial activities, irrigation with sewage and the excessive use of pesticides and fertilizers) [3] [4] [5]. Heavy metals contamination of agricultural soils is initiated by farmers, whose economic production depends on the use of agricultural chemicals and fertilizers and irrigation water [6]. Generally, the presence of these toxic elements in the soil and agricultural crops are associated with the use of fertilizers and the presence of ions that can bind these metals [7].
On the other hand, repeated applications of animal manure compost probably increase the concentrations of Zn, Cu, Cd and Hg in the soil [8] [9]. Pesticides also contain heavy metals such as As, Cr, Co, Pb, Ni [10] and these chemicals are used by farmers to control pests and diseases. Heavy metals are transferred from the abiotic environment to living organisms, accumulate in biota at different trophic levels, and therefore contaminate food chains with implications in human health and wildlife [11] [12]. Heavy metals presence such as Cd, Cr, Cu, Mn, Ni, Pb and Zn in food is one of the most harmful health problems in the world due to its non-biodegradable nature, persistence and toxicity [13] [14] [15]. People are exposed to heavy metals and metalloids through ingestion, inhalation, and dermal contact [16]. Therefore, contamination of the food chain is one of the important pathways for the entry of these toxic contaminants in the human body which can cause health risks [17].
Health risks from heavy metals associated with the consumption of native potato is a very important issue, considering that Peru is the largest potato producer in Latin America and the twelfth in the world with 4.5 million tons per year [18]. Native potatoes represent a subsistence means for small farmers in the high Andean areas [19]. It is the main crop and a staple food of the high Andean population. In 2015, potato consumption in Peru reached 85 kg/person [20]. The native potato is cultivated in the mountains of Peru, especially in peasant communities above 3000 meters above sea level. Native potatoes have a high nutritional value, with a high content of proteins, vitamins C, B6, B1, folic acid, minerals such as potassium, phosphorus, calcium and magnesium, and micronutrients such as iron and zinc [21]. Some researchers from China, Pakistan and Slovakia have studied toxic metals in potatoes such as [22] [23] [24] [25]. They reported high contents of Cd and Pb in contaminated areas that in some cases exceeded the food safety standards.
In Junín, Peru reported Pb contents in white or improved potatoes above rec-  [26]. In Peru, heavy metals contamination is a serious problem caused by mining activities leading to a chronic environmental impact due to the release of chemical residues, tailings, toxic gas, dust, acid drains and irreversible destruction of the ecosystem. In a nearby mining operation of La Oroya located in the central highlands, currently there are evidences for deterioration of water quality, air, soil, and fauna [27]; and is considered among the most dangerous for human health, due to their high concentrations of polluting and toxic products [28]. In this context, investigating the heavy metals content in native potatoes grown in Andean zones above 3800 m is a concern; considering it as a daily food for the Andean population. The objective of this research was to evaluate the concentrations of heavy metals in soil and accumulation in the tubers of two of native potato varieties ("peruanita" and "huayro macho") of major consumption, and to assess the potential of non-carcinogenic and carcinogenic risk in the health of the high Andean inhabitants from Junín department, Peru.

Study Area
The study area is located in the central highlands of Peru, which includes the districts of Quilcas, Comas, Ricran and San Juan de Jarpa, within the provinces of Huancayo, Concepción, Jauja and Chupaca respectively, all located in the department of Junín ( Figure 1). This area is one of the most representative for native potato cultivation and it is located at altitudes that range from 3000 to 4200 masl, between 11˚32'26.855" and 12˚ 8'5.525" south latitude; and 75˚28'28.422" and 74˚56'46.401" west longitude. The climate in this area is humid cold with maximum temperatures of 18˚C to 24˚C and minimum temperatures of −5˚C to 10˚C; with an annual precipitation that varies from 700 to 1170 mm. The two native potato varieties "peruanita" and "huayro macho" are planted in a mixture, in rolling terrains with slopes of 30%. The main economic activity of the families is agriculture and the raising of sheep, llamas and alpacas. Native potato production is for self-consumption and seed. A small portion of the production is sold in local markets and some in supermarkets, generating a small-scale income for rural families. water to remove soil particles and surface contaminants, and rinsed with distilled water and subjected to a drying process at room temperature. Composite soil samples of 1 kg each were collected from the same selected plots, at a depth of 0 -20 cm. The soil samples were filled in hermetic polyethylene bags, labeled and transported to the laboratory. Previously, materials such as pebbles, small stones and organic remains were removed.
In the laboratory the digestion phase was carried out, previously the potatoes with clock moons and were subjected to 150˚C until they become pasty, then the solution was cooled to room temperature, then the residues were diluted with deionized water after stirring, they were emptied into 100 ml flasks, at they were then filtered with No. 42 filter paper and the samples were stored in the refrigerator at 4˚C before analysis. The heavy metals concentrations were determined using the atomic absorption spectrophotometer (Varian Model AA240). Before the analysis of the metals, the instrument was calibrated using standard solutions, which were supplied by Merck to establish the standard calibration curves for each metal.

Questionnaire
A questionnaire was developed to determine the average daily intake rates of native potato by the inhabitants of each study place. A questionnaire was applied to 65 peasant families in order to extract information on the amount of native potato intake per day, frequency of intake, age and weight of children and adults. A representative of each family among men and women over 18 years of age in the four localities were surveyed.

Bioconcentration Factor
The bioconcentration factor (BCF) measures the translocation capacity of the heavy metals from the soil to the edible part of the crop plants [30]. Metal concentrations in the soil and tubers were calculated on the basis of their fresh weight. The BCF of As, Cd, Fe, Pb and Zn were calculated using the following

Human Health Risk Assessment
Human health risk assessment is a common method of quantifying the nature and likelihood of adverse health effects in humans who are exposed to certain heavy metals [33]. To assess the risk to human health of heavy metals, the level of human exposure to this metal should be calculated following the route of exposure of the contaminant to the human body: The estimated daily intake of metals (EDIM) through food was calculated using the following Equation (2) where EDIM represents the estimated daily intake of metals (mg/kg/day), Cm is the concentration of the metal in the tuber (mg/kg), Cf is the conversion factor

Non-Carcinogenic Risk Assessment
Non-cancerous risks are assumed to exhibit a threshold below which adverse effects on human health are not expected to be a concern [39]. The health risk caused by exposure to non-carcinogenic heavy metals from food intake was calculated by the threshold hazard quotient (THQ). THQ for each metal was calculated according to the following Equation (3) [35] [36]: where: C is the concentration of heavy metals in the tuber (mg/kg); IR is the

Statistical Analysis
Means, standard deviations, minimum and maximum values of heavy metals concentrations in soil and tuber samples were calculated. The two-way ANOVA was used to detect significant differences in heavy metals concentrations between varieties and localities, and the comparison of means was performed using the Tukey test with a significance level of 0.05.

Concentration of Heavy Metals in Soils
The concentrations of heavy metals in soil samples obtained from native potato fields are presented in  [46] and that established by China [22]. However, significant variations in the content of metals in the soil were observed between the places studied. Higher concentrations of As, Pb, Fe and Zn were observed in the following order: Quilcas > Ricrán > Jarpa > Comas. The presence [10] [47] and to air pollution [48]. Therefore, it is very important to determine the sources, distribution and level of contamination of the high Andean soils. The bioconcentration factor (BCF) measures the ability of metals to move from the soil to the tuber, BCF of heavy metals in the tubers is shown in Figure   2. BCF values were higher for Cd and Zn compared to the other metals studied because these elements are readily absorbed, especially Cd element [51]. No significant differences in BCF were observed for As, Cd, Pb and Zn between the two varieties of native potato except for Fe. The highest BCF value was registered for Fe in the "huayro macho" variety. The sequence of BCF values for metals in native potato was found in the following decreasing order: Zn > Cd > Pb > As >

Estimated Daily Intake of Metals
When estimating the levels of exposure to heavy metals in the human population is very important to assess the health risk of any contaminant in the daily intake of food. The estimated daily intake of metals (EDIM) in adults and children in the four districts is shown in Table 3. The daily intake of Zn and Fe was higher in children (0.068 and 0.014 mg/kg/day) than in adults (0.047 and 0.011 mg/kg/day). These results were lower than the reference doses (0.7 and 0.30 mg/kg/day). A study in Pakistan found similar results in potatoes [22]. The decreasing order of daily heavy metals intake for children and adults was as follows: Fe > Zn > Pb > As > Cd with values less than 0.1. In a nearby area of Zn smelting facility in China, values less than 0.01 were reported in potato intake [23]. The daily intake of heavy metals was below the provisional maximum tolerable daily intake (PMTDI) for Fe (0.8 mg/kg/day) and Zn (0.3 -1.0 mg/kg/day) and tolerable weekly intake provisional (PTWI) for As (0.015 mg/kg), Cd (0.007 mg/kg) and Pb (0.025 mg/kg) as recommended by Food and Agriculture Organization and World Health Organization (FAO/WHO) [53] [54] [55]. Therefore, we can safely assume that there is not a health risk for native potato consumers. The Fe and Zn contents in native potatoes are essential trace elements required by humans in essential biochemical processes, and they are not a threat when the intake is within the permitted limits.   [56]. The TCR values of As were greater than the critical value of 1 × 10 −4 for children and adults, therefore they were not within the safe range, which means that the intake of native potatoes represents a lifetime cancer risk for children and adults associated with the ingestion of contaminated foods with this toxic element. In the town of Quilcas, higher TCR values were found for the three metals, which would be associated with excessive and prolonged consumption of native potatoes. The finding of these results is of concern about the possible cancer risk of As for residents in the four districts studied in the Junín region, considering that As can cause skin, bladder and lung cancers [59].

Conclusion
The highest concentrations of heavy metals in agricultural soils of four highland Andean locations in Peru were observed for Fe, with a decreasing order of other heavy metals: Zn > Pb > As > Cd. The contents of the selected heavy metals in native potatoes were below the safe limits with exception of Pb. The bioconcentration factor trend for the two native potato varieties was in the following order: Zn > Cd > Pb > As > Fe. The estimated daily intake of metals in adults and children through the consumption of native potato was higher for Fe and Zn.
The hazard index and threshold hazard quotient values of heavy metals were found within the safety limits. Children were more susceptible to heavy metals contamination than adults. The inhabitants of the four high Andean zones were exposed to carcinogenic health risks for As through daily intake of native potatoes. The carcinogenic risk for As was greater than the critical value of 1 × 10 −4 .
Therefore, it is suggested to carry out a continuous and systematic monitoring of heavy metals in soils and native food crops, especially As, and to study the sources of contamination for implement a soil and crop management program to guarantee the quality of food products.