Risk of exposure to metals in soil contaminated by steel industry waste for a population in Volta Redonda, RJ

The aim of this study was to identify the risk of population’s exposure, by different exposure routes, to Zn, Ni, Cu, Cr


INTRODUCTION
The socio-environmental impacts caused by the steel industry have fostered scientific discussions and research on the relationship between humans and the environment, as well as its consequences on a global scale (Masindi and Muedi, 2018).
The production processes in the steel industry release a wide variety of hazardous chemicals, posing high risks for the environment and consequently to the health of living beings (Rosenfeld and Feng, 2011).Thus, this type of industry can generate several occupational and socio-environmental risks.It demands a high amount of energy to process input products to obtain steel, which generates a large amount of waste, such as dust, blast furnace mud, steelmaking slag, coal fines, etc. (CETEM, 2013a).
The release of these substances is mainly during the transport and storage of raw materials (charcoal and ore), vehicle traffic, coconut shell charcoal production (loading, coking, oven pushing, and steam generation), sintering (sintering machine), blast furnace (air blowing and heating), steelmaking, casting, and thermoelectric power station (CETEM, 2013a).
Steelmaking slag is an important metallurgical solid waste whose chemical composition may vary according to the raw material used, production process, conversion coating, type of steel produced, and slag cooling and storage, forming calcium silicates and ferrites combined with cast-iron oxides, aluminum, manganese, calcium, magnesium, among other chemical substances (Zhang et al., 2014).The solid waste generated in the process of steelmaking must be treated before its disposal, since even steelmakers with effluent treatment plants cannot eliminate pollutants, only transfer them, transforming effluents into solid waste (CETEM, 2013a).
Volta Redonda is home to one of Latin America's largest steel companies.However, reports of irregularities have attracted the attention of the media and the Federal Public Ministry since its inauguration.This company donated a plot of land to the employees to build a condominium.Until then, the steelmaker had used this land to dispose of tons of hazardous waste, neglecting regulations and environmental licensing processes (Brasil, 2012;CETEM, 2013b).The company has deposited large amounts of steel slag on the site next to the houses since that time.Not only was the condominium built over industrial waste, but it also is located within less than 30 meters from the area currently used for storing and processing steelmaking slag (Brasil, 2015).Nowadays, a 30-meter-high "pile" of waste outgrows the site's walls, and it is less than 50 meters from the Paraíba do Sul River.
For this study, we selected the elements zinc, nickel, copper, chromium, and lead due to their widespread use within the steel industry and their toxicity.Although an essential element in the human body, zinc levels above the maximum permissible limits may induce hematological, respiratory, gastrointestinal, neurological, immunological, dermal, ocular, and systemic effects (Plum et al., 2010).Accumulation of Ni and its compounds in the body through chronic exposure can affect the cardiovascular and respiratory systems, skin, liver and induce genotoxic, teratogenic, and carcinogenic effects (Soares et al., 2011;Genchi et al., 2020).Like zinc, copper is an essential element for human beings.However, levels above the maximum permissible limits may induce neurological, psychiatric, hematological, or hepatic effects (Sócio et al., 2010).Chromium is an important causative agent of contact dermatitis among workers, and it can also cause chronic skin ulcers and nasal septum perforations due to its corrosive properties.Trivalent chromium is an essential nutrient in humans, whereas chronic exposure to Cr (VI) compounds is mainly associated with carcinogenic effects (Singhal et al., 2015).Lead is a highly toxic metal, even at trace exposure levels, responsible for severe damage to the nervous, hematological, renal, cardiovascular, gastrointestinal, and reproductive systems (Sall et al., 2020).The International Agency for Research on Cancer (IARC) classifies chromium (Cr) and nickel (Ni) as Group 1, carcinogenic to humans, being mainly associated with lung, nasal, and nasopharyngeal cancer.In turn, lead (Pb) is categorized as Group 2A, probably carcinogenic to humans, as only the evidence in animals is conclusive.Metals demonstrate a high tendency to bioaccumulate in the environment.These elements often exist at low concentrations, but anthropic activities commonly induce high concentration levels (IARC, 2012).
This study aimed to estimate the risk to human health through multi-pathway exposure routes caused by metal concentrations (Zn, Ni, Cu, Cr, and Pb) in soil samples from nonwaterproofed public areas in a condominium of Volta Redonda -RJ.

Study area
The evaluated site was a condominium in Volta Redonda, a municipality in the Vale do Paraíba microregion, Southern Rio de Janeiro (182,483 Km 2 ), on the Rio -São Paulo axis.The Paraíba do Sul River crosses the municipality, flows west to east, and is the primary source of water supply for more than 12 million people in the state, among which 85% are metropolitan region residents.The region's upland areas present deep, acidic clay soils with low porosity; in turn, lowland areas at the riverbanks are predominantly composed of fertile soils rich in organic matter.The municipality has a population of 257,803 inhabitants, with 1,412.75inhabitants per Km 2 .The condominium is located in the Santo Agostinho neighborhoodin the east part of the municipality, between the right Paraíba do Sul riverbank and the Lúcio Meira highway (BR-393).It consists of 808 properties, divided into eight blocks, with approximately 3,000 dwellers.According to INEA, the area is classified as a contaminated area under intervention (ACI) (INEA, 2014;Brasil, 2012;2015).

Soil sampling
Approximately 4-meter-high walls separate the condominium blocks.All sidewalks, streets, backyards, blocks, and squares were waterproofed so the population would not have direct contact with the soil.The collection of superficial and underground soil samples in nonwaterproofed public areas of the condominium contributed to analyzing the area's current situation, mainly in its surroundings, considering the distance from the steelmaking slag landfill.
Soil sampling took place at the same six points in three campaigns (Figure 1).The points were georeferenced, and soil surface samples ("A") were collected at an average depth of 0.20 m, and underground samples ("B") at a mean depth ranging between 2.00 and 3.00 m, depending on the water level.During collection and transport to the laboratory, samples were kept in duly identified glass bottles (1000 mL) and refrigerated-stored in a thermal box at 4ºC.The first campaign was carried out on a sunny day in June 2018 with a temperature of 32ºC.Although the rains are constant in the city regardless of the season, one of the driest months in Volta Redonda is June.The average wind speed was 13.2 km h -1 in the northnortheast direction.
The two other campaigns were executed in September 2019 and May 2020.In both samplings, the days were cloudy.In September, the climate conditions were a temperature equal to 20ºC and an average wind speed of 9.2 km h -1 in the south direction.The sampling in May experienced intermediate conditions with a temperature of 25ºC and average wind speed of 10.5 km h -1 in the northern direction.
The land slope causes the water to seep through the condominium's waterproofed canals (streets, sidewalks, squares, blocks) towards the Paraíba do Sul River during rainfall periods.Sampling points were delimited based on the fluid contamination path during precipitation and the distance from the steelmaking slag landfill, considering those closer to the "pile" (Points 2 and 3), intermediate points (Points 1 and 4), and those further away (Points 5 and 6).A shelltype hand auger (ABNT, 2007) of 4" nominal diameter performed the soil sampling.
A mixture of nitric and hydrochloric acids digested the soil samples, and the solution was heated to reduce volume.Filtration was then carried out, and deionized water completed the volume.After the digestion process of the samples, the ICP OES performed the determination of the total metal content.The acid digestion used as a pretreatment followed the EPA Method 3005A -"Acid digestion of waters for total recoverable or dissolved metals for analysis by FLAA or ICP spectroscopy".Calibration curves were prepared using blank samples spiked with adequate micro-volumes of the standard solutions for each metal, and laboratory-made reference materials checked the accuracy of the procedure.Limits of detection (LOD) and quantification (LOQ) of the method were 0.07 and 0.25 mg Kg -1 , respectively.

Health risk
The potential carcinogenic and non-carcinogenic risks that may arise from the exposure of adults and children living in the study area to metals in the soil were determined by combining exposure pathways.These risk pathways involve acceptable daily intake (ADI) of metals (mg Kg -1 ) through ingestion (Ing), inhalation (Inal), or dermal exposure (Derm) using the methods described in Equations 1, 2, and 3 (Lange, 2018;Bwatanglang et al., 2019).(3) ADIIng represents the ingestion pathway, ADIInal inhalation, and ADIDerm dermal contact.Other parameters and their corresponding functions are described in Table 1.The exposure factors used in this study are based on the study carried out by Gabarrón et al. (2017).The hazard quotient (HQ) was used to analyze the potential non-carcinogenic effect of metals in soil samples, relating ADI with its reference dose (RfD) (Table 2) for each exposure and contaminant pathway (c), as described in Equation 4 (Lange, 2018;Bwatanglang et al., 2019).As described in Equation 5, the health index (HI) for various contaminants, expressed as HQ sum for each contaminant (c), describes the non-carcinogenic cumulative effect of their combination in soil samples (Lange, 2018;Bwatanglang et al., 2019).HI = Σ HQ c = HQ Ing + HQ Inal + HQ Derm (5) The cancer risk index (CRI) represents the likelihood of an individual developing any cancer throughout his or her lifetime and is calculated by combining ADI with each contaminant (c) cancer slope factor (CSF).Equation 6describes such an index (Lange, 2018;Bwatanglang et al., 2019).
Equation 7 provides a complete picture of an individual's lifelong cancer risk by combining all metals and exposure pathways (Lange, 2018;Bwatanglang et al., 2019).
TCRI represents the combined effect for each exposure pathway, TCRIc is the combined effect for each exposure pathway and each contaminant (c), CRIIng exposure by ingestion, CRIInal by inhalation, and CRIDerm by dermal contact.

Metal concentrations in soils
Table 3 shows averages and standard deviations for Zn, Ni, Cu, Cr, and Pb concentrations in soil samples from non-waterproofed public areas of a condominium in Volta Redonda -RJ.Resolution n o .420/2009, from the National Environment Council (NEC) in Brazil, establishes three classes of guiding values for soils, the quality reference value (QRV), the prevention value (PV), and the intervention value (IV).QRV is the concentration of a certain substance, which defines soil as clean, used as a reference in the prevention and control of contamination.PV is the concentration above which harmful changes in soil quality can occur, with consequences for humans and animals, and preventive measures against contamination must be used.Finally, IV is the concentration above which there are potential risks to human health.However, each state establishes its own QRV.The Company of Technology and Basic Sanitation of the State of São Paulo (CETESB) prepared a list with guiding values for the concentration of metals, among others, in soil, which will be used for comparing since they are the same as NEC, except the QRV (CETESB, 2016).
To obtain the human health risk indices after the exposure to the contaminated soil by any exposure pathway, metal concentrations in the surface soil were also compared to permissible levels (PL) in food for human consumption.PL for agricultural soils could be harmful to human health in case of ingestion, inhalation, or contact with the skin (Tóth et al., 2016;Bwatanglang et al., 2019).
Zinc average concentration in surface samples ranged from 36.3 to 130.5 mg Kg -1 , much higher than those established by the Food and Agriculture Organization/World Health Organization (FAO, 2011), of 2.0 mg Kg -1 , as well as the QRV (60 mg Kg -1 ) and PV (86 mg Kg -1 ) from CETESB, except Point 6A (CETESB, 2016).A study carried out in the cities of Mariana and Barra Longa, Minas Gerais State, assessed the health impacts of Fundão Dam breach-derived metals using surface soil samples.The authors found zinc concentration to range from 0.01 to 18.62 mg Kg -1 in Mariana and 0.01 to 32.35 mg Kg -1 in Barra Longa, values well below those found in the condominium (Silva et al., 2019).In Nigeria, a study was conducted to investigate the health impacts of traffic-derived metals using surface soil samples.The authors found zinc concentration to range from 6.72 to 13.57 mg Kg -1 , also values well below those found in the condominium (Bwatanglang et al., 2019).However, two other studies also conducted in Nigeria reported much higher concentration levels.One of the studies (Tsafe et al., 2012) found values equal to 68.91 mg Kg -1 , while the other (Ogundele et al., 2015) obtained a zinc concentration range between 30.8 and 219.23 mg Kg -1 , similar to or higher than the findings in Volta Redonda.
The FAO (2011) has established a value of 0.20 mg Kg -1 for nickel concentration, much lower than those found in surface samples ranging from 7.7 to 20.3 mg Kg -1 .On the other hand, CETESB has established QRV and PV equal to 13 and 30 mg Kg -1 (CETESB, 2016), respectively, which means that the levels found in such samples are following the legislation.Nickel values reported in both studies from MG, Mariana (0.05 to 4.59 mg Kg -1 ) and Barra Longa (0.005 to 13.49 mg Kg -1 ), and the other from Nigeria (1.83 to 14.87 mg Kg -1 ) were similar to or lower than those found in the condominium (Silva et al., 2019;Ogundele et al., 2015).Another study also developed in Nigeria found nickel concentration in surface soil samples ranging from 0.16 to 0.42 mg Kg -1 , values well below those present in the condominium (Bwatanglang et al., 2019).
The average copper concentration in surface samples was much higher than 0.20 mg Kg -1 established by the FAO ( 2011), but well below 35 (QRV) and 60 mg Kg -1 (PV) accepted by CETESB (CETESB, 2016), ranging from 11.8 to 28.1 mg Kg -1 .The studies conducted in Mariana and Barra Longa also reported copper concentrations below those found in the condominium.The copper concentrations ranged from 0.002 to 8.29 mg Kg -1 in Mariana and 0.002 to 10.32 mg Kg -1 in Barra Longa (Silva et al., 2019).Copper concentrations (0.14 to 0.17 mg Kg -1 ) in another study from Nigeria were well below those found in the condominium (Bwatanglang et al., 2019).In turn, another investigation from the same country reported a concentration range between 4.83 and 80.13 mg Kg -1 (Ogundele et al., 2015), values similar and much higher than our results.
Average chromium concentration in surface samples ranged from 36.7 to 70.5 mg Kg -1 .According to CETESB, QRV is equal to 40 mg Kg -1 , while PV is 75 mg Kg -1 (CETESB, 2016).Therefore, the levels in such samples comply with the current legislation.On the other hand, those values are much higher than 0.50 mg Kg -1 , accepted by the FAO (2011).Two studies carried out in Nigeria reported chromium levels lower than those found in the condominium.Their results were equal to 16.73 mg Kg -1 (Tsafe et al., 2012) and ranged from 0.01 and 0.07 mg Kg -1 (Bwatanglang et al., 2019).However, another reported chromium concentrations between 10.57 and 77.10 mg Kg -1 (Ogundele et al., 2015), comprising lower, similar, and higher values than in the current research.
Lead average concentrations in surface samples ranged from 12.2 to 23.2 mg Kg -1 , which is also according to the QRV (17 mg Kg -1 ) and PV (72 mg Kg -1 ) (CETESB, 2016).However, these values are much higher than those established by FAO (2011), 0.35 mg Kg -1 .In Mariana and Barra Longa, lead levels found were similar and lower than those from Volta Redonda.In such cities, lead concentrations varied from 0.005 to 12.63 mg Kg -1 in the former and 0.005 to 8.47 mg Kg -1 in the last one (Silva et al., 2019).Three studies in Nigeria assessed the lead concentration in surface soil samples.All samples presented an average concentration of 0.86 ± 0.06 mg Kg -1 , well below that found in the condominium (Bwatanglang et al., 2019).However, the other two reported values, 29.66 mg Kg -1 (Tsafe et al., 2012) and a concentration range from 24 to 157.66 mg Kg -1 (Ogundele et al., 2015), are higher than in Volta Redonda.

Health risk indices
Table 4 presents the acceptable daily intake (ADI) by metal and exposure pathway for adults and children.In turn, Tables 5 and 6 highlight the possible non-carcinogenic and carcinogenic risks for Zn, Ni, Cu, Cr, and Pb in superficial soil samples from a condominium in Volta Redonda by different exposure pathways (ingestion, inhalation, and dermal).
Based on the exposure factors listed in Table 1, we found the ADI by metal and exposure pathway (Table 4) for adults and children to be lower than the reference dose (RfD) (Table 2).The acceptable daily intake for the three pathways increased in the following order: ADIInal < ADIDerm < ADIIng for adults and children.Comparing the ADI for children and adults shows that the acceptable daily intake for children is lower by ingestion and dermally, which means that this age group is more susceptible to these routes.The acceptable dose intake for adults will already pose a risk to the health of children.The studies conducted in Nigeria and São Paulo reported the same results, finding children more susceptible to a higher level of exposure dose than adults (Lange, 2018;Bwatanglang et al., 2019).

Figure 1 .
Figure 1.Soil samples collection points in the Volta Redonda condominium.Source: Google Earth, 2019.

Table 1 .
Exposure factors used to identify health risk through different soil exposure pathways.

Table 2 .
Each metal reference dose (RfD, mg Kg -1 ) and cancer slope factor (CSF) by exposure pathway.

Table 3 .
Average (mg Kg -1 ) and standard deviation for metals concentration in soil samples of a residential condominium in Volta Redonda, RJ.

Table 4 .
Acceptable daily intake (mg Kg -1 ) by metal and exposure pathway for adults and children in a Volta Redonda condominium.Soil concentration; UCL: Upper confidence limit; ADIIng: Acceptable daily intake by ingestion; ADIInal: Acceptable daily intake by inhalation; ADIDerm: Acceptable daily transdermal intake.

Table 5 .
Non-carcinogenic hazard quotient (HQ) by metal and exposure pathway for adults and children in a Volta Redonda condominium.

Table 6 .
Cancer risk index (CRI) by metal and exposure pathway for adults and children in a Volta Redonda condominium.
CRIIng: Cancer risk index by ingestion; CRIInal: Cancer risk index by inhalation; CRIDerm: Cancer risk index by dermal; TCRI: Combined effect for each exposure pathway.