Lead in soil and vegetables in a glazed ceramic production area: A risk assessment
Introduction
Environmental components, i.e. food, water, sediments, soil, air, and biota (including humans), may be exposed to lead (Pb) contamination (Fu and Ma, 2013; Zhou et al., 2016; Costa et al., 2017). Pb is a toxic metal and a ubiquitous contaminant in the environment; Pb is not biodegradable, and does not have any physiological function in living organisms (Virdy et al. 2007; Reddy et al., 2014). Among the sources of human Pb exposure, the diet has an important role (Zaza et al., 2015); however, there are other sources as well, such as mining and industrial activities (Molina-Villalba et al., 2015), ceramic glazing (Yaylali-Abanuz, 2011; Costa et al., 2017; Diaz-Ruiz et al., 2017), improper disposal of potentially contaminated industrial waste (Luo et al., 2011), and domestic waste burning (Menezes-Filho et al., 2011; Shaheen et al., 2016).
Lead occurrence in the environment has caused increased concern about food safety, since vegetables cultivated in Pb-contaminated areas can absorb this metal from the soil (Sipter et al., 2008). Several studies demonstrated the contamination of vegetables through the transfer of Pb from the soil (McBride et al., 2013, 2014; Xiong et al., 2014). Due to vegetable contamination, the consumption of these products can have adverse effects on human health, since contamination of the food chain is one of the main sources of human exposure to toxic metals such as Pb (Pan et al., 2016; Rehman et al., 2018).
After ingestion, Pb is absorbed and directly available in the bloodstream and can cause a wide range of adverse outcomes to human health. Nervous, renal, cardiovascular, and reproductive system disorders due to Pb molecular interferences in these systems are well described in the literature (Haefliger et al., 2019; ATSDR, 2007). Children are more susceptible to Pb due to factors such as “hand to mouth” habits (Menezes-Filho et al., 2018), high absorption rates of Pb by the digestive system (Luo et al., 2012), and maternal-fetal transfer (Lin et al., 2010). In addition to the fact that children are the more likely exposed group, they are more susceptible to the toxic effects of Pb due to the immaturity of the blood-brain barrier (Flora et al., 2012), presenting neurological impairments such as cognitive deficit, maladaptive behavior, hyperactivity, encephalopathy, and death (Lubran, 1980; Haefliger et al., 2009; AAP, 2016).
Considering that Pb is a xenobiotic, it does not have any essential function in the human body (Perez-Fernandez et al., 2019), and even at low concentrations can have deleterious effects on human health (Menezes-Filho et al., 2018). Therefore, the occurrence of Pb in food or the bloodstream may represent a public health issue. Recently, Menezes-Filho et al. (2018) demonstrated that children in the age range of 6–12 years with low blood Pb level (median and IQR of 2.4 (0.3–2.8) μg/dL) had significant IQ deficits, especially those more exposed to Mn from the emissions of a ferro-manganese alloy plant in Bahia, Brazil.
To assess the risk due to the consumption of specific foods or food groups, or the diet of a population, the United States Environmental Protection Agency (US EPA) has established the target hazard quotient (THQ) associated with contaminants such as Pb. This concept includes a health risk assessment (non-carcinogenic) associated with a contaminant of interest based on the oral reference dose (RfD), as the maximum allowable limit for consumption during a lifetime. Even though, the established daily RfD for Pb (4 μg/kg) is no longer in use, since a threshold for this element cannot be established. Our limited data collection prevented using more comprehensive approache.
Maragogipinho is a district of Aratuípe, a town located at the Reconcavo Baiano, 90 km from Salvador, the state capital in Brazil (Fig. 1). The local economy is based on artisanal production of ceramic utensils and clay handicrafts, in which artisans glaze the utensils using lead oxide (PbO) as a flux (Pinho Neto, 2008). To glaze the ceramics, it is necessary to obtain the PbO artisanally by melting metallic Pb obtained from automotive batteries. This process is carried out by artisans at rudimentary bonfires for approximately two hours. This oxide is then mixed with a clay suspension in water and applied to the internal surface of the ceramic. Then, it is fired again, forming a glaze that guarantees waterproofing and shine to the ceramic piece.
The lack of adequate training of artisans, poor infrastructure for processing this hazardous product, and the disposal of broken parts of the glazed ceramic in the environment can pose a greater risk of Pb contamination in the environment, as suggested by Hatje and Barros (2012) and Costa et al. (2017). During the glazing process, the fired Pb is dispersed as fine particulate matter carried away with smoke, which may contaminate the soil and subsequently the vegetables by deposition. In addition to dust deposition onto the soil and vegetables, vegetables can absorb Pb from the soil, thus characterizing a possible exposure source.
Considering the lack of studies in this area, the need to investigate possible environmental Pb contamination, and consequently the health risks to the population, the current study assessed the health risk due to the consumption of the most cultivated vegetables in this region by the population. Thus, the aims of this study were:i) evaluate whether pottery activity has an impact on Pb levels in the soil and vegetables cultivated in the region; ii) estimate the transfer factor of Pb in soil to vegetables; and iii) perform an assessment of health risk resulting from exposure to Pb due to the consumption of the most cultivated vegetables by local residents and based on the THQ.
Section snippets
Study materials
Forty-four samples of surface soil, eighteen samples of cassava root, seven samples of coriander, fifteen samples of banana, and thirteen samples of papaya were collected in backyards or gardens of the residences in the study area during two sampling periods, with the first in September 2017 (dry season) and the second in March 2018 (rainy season). The soil samples were collected at a depth of approximately 15−20 cm in the root zone of the collected vegetables. To measure the depth, graduated
Concentration of Pb in soil
The median, interquartile range, minimum, and maximum concentrations of Pb in the soil are shown in Table 2. Of the forty-four soil samples analyzed, Pb concentrations ranged from 0.47 to 106.14 mg.kg¹ with a median of 13.35 mg.kg-¹. The median Pb concentration of samples collected during the dry period was 15.44 mg.kg-¹, ranging from 0.47 to 106.14 mg.kg-¹. The samples collected during the rainy season had a median concentration of 12.17 mg.kg-¹, ranging from 2.47 to 82.84 mg.kg-¹. No
Conclusions
The study revealed that although Maragogipinho village has a history of Pb use by artisans, the average Pb levels in soil and vegetables were below the maximum limit established by the regulatory agencies in Brazil and abroad. Owing to the low mobility of Pb from soil to vegetables and the fact that airborne Pb particles are heavier, only proximal soil and vegetables showed higher Pb content. THQ assessment showed that the risk associated with Pb intake via the consumption of vegetables
Funding
This study was partially supported by “Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)” of the Brazilian Government and from the “Fundação de Apoio a Pesquisa do Estado da Bahia (FAPESB)” under grant No. SUS0040/2018.
CRediT authorship contribution statement
Erival Amorim Gomes-Júnior: Conceptualization. Homegnon Antonin Ferreol Bah: . Ynayara Joane de Melo Rodrigues: . Matheus de Jesus Bandeira: . Nathalia Ribeiro dos Santos: . José Antonio Menezes-Filho: Conceptualization.
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgments
The authors would like to thank the residents of Maragogipinho Village for participating in the study, CAPES (Coordination for the Improvement of Higher Education Personnel) for the master’s program scholarship and a special thanks to the Laboratory of Toxicology of the Federal University of Bahia staff for the support provided during the sample collection, processing and analysis.
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