SEGH Articles

Exposure to Arsenic And Other Toxic Elements Through Eating Earth

01 February 2012
The practice of deliberately eating earth, known as geophagy has been common in many cultures across the world. Unfortunately, very little scientific research is being conducted in this area and its impact on human health.

 

 

The work decribed below has been published and can be accessed from the following link: http://www.ehjournal.net/content/9/1/79

The practice of deliberately eating earth, known as geophagy has been common in many cultures across the world.  It continues to be practiced today in many parts of the world including amongst certain groups within the United Kingdom.  The reason behind this practice remains unknown, although it has been suggested it is consumed for nutritional and medicinal purposes. Since geophagy is more prevalent during pregnancy, it has been suggested that eating earth may remedy deficiencies that results in anaemia in women.  However, others argue that eating earth may cause anaemia.   Unfortunately, very little scientific research is being conducted in this area and little is known about the composition of earth that is consumed in different parts of the world and their impact on human health.   The mineral content of the earth will naturally vary from region to region and the potential of exposure to toxic elements is likely.   This is a cause for concern especially in certain parts of the world where there are environmental problems resulting in the presence of elevated levels of toxic elements such as arsenic in water and the food chain.  Arsenic is a toxic element that is present at high levels in drinking water in Bangladesh and India.  Although many studies have focused on arsenic exposure in India (West Bengal) and Bangladesh through drinking water, very little work has been done to consider other sources of exposure.  Exposure to arsenic through consumption of rice and vegetables has been highlighted (Cascio et al. 2011 and references therein).  It was reported that the Bangladeshi's residing in the United Kingdom are exposed to a higher level of arsenic compared to white Caucasians (Cascio et al. 2011) due to their high intake of rice. 

Shaban Al-Rmalli is a PhD student (PhD supervisors:  Parvez Haris & Richard Jenkins, De Montfort University; Collaborator:  Michael Watts, British Geological Survey) at De Montfort and his research project was to identify the different sources of arsenic exposure in the Bangladeshi community not just from rice and vegetables.   The aim of the project is to identify sources of exposure to toxic elements that may explain the reasons underlying the disproportionately higher prevalence of different disease including diabetes, cardiovascular disease and some types of cancer amongst UK Bangladeshis (Cascio et al.  2010 & references therein).   Information obtained could be used to help modify the diet of the Bangladeshis (both in the UK and in Bangladesh) so that they avoid certain types of foods/non-foods that may contain high levels of toxic elements.  As part of his PhD project, Shaban analysed over 1,000 Bangladeshi food and non-food samples.  Amongst the samples he purchased from ethnic Bangladeshi shops in the United Kingdom was baked clay (imported from Bangladesh) that are called Sikor in Bengali (see Figure).   Discussions with the members of the Bangladeshi community and shop keepers revealed that these clay tablets are purchased mainly by Bangladeshi and African women and especially by pregnant women from these communities.  This revelation was rather alarming and further investigation into this issue revealed that in Bangladesh some women can consume as much as 500g of these clay tablets per day.   The average weight of the sikor tablets shown in the Figure is approximately 15g and most women consume between 3-4 tablets per day.  This is particularly worrying as intake of high levels of toxic elements could not only harm the health of the pregnant women but that of the unborn baby since many toxic elements including lead and arsenic can transfer from the mother to the baby through the placenta.  What was a cause for further worry is that women in Bangladesh are already being exposed to high levels of arsenic and manganese etc through drinking water and consumption of sikor may potentially lead to a further increase in exposure to these elements.   It was therefore vital that such samples are analysed to evaluate their content of arsenic as no previous studies have considered this issue.   

Sikor samples, originating from Bangladesh,  were purchased and analysed for their As, Pb, Cd, Mn, Fe and Zn levels using ICP-MS. Furthermore, detailed As speciation analysis was performed using HPLC-ICP-MS (http://www.ehjournal.net/content/9/1/79).   The levels of As (3.8-13.1 mg kg-1), Cd (0.09-0.4 mg kg-1) and Pb (21-26.7 mg kg-1) present in the sikor samples were of concern and could have detrimental effect on the health of the consumer. Speciation analysis revealed that sikor samples contained mainly the toxic inorganic As. It was calculated that modest consumption of 50 g of sikor is equivalent to ingesting 370 μg of As and 1235 μg of Pb per day, based on median concentration values. Just consuming 50g sikor per day exceeds the permitted maximum tolerable daily intake (PMTDI) of inorganic As by almost 2-fold (http://www.ehjournal.net/content/9/1/79).   The study concluded that sikor consumption can be a source of exposure to As, Cd and Pb in some Bangladeshis and in some other populations where this is consumed such as in India & Africa.   In the future, it is important to evaluate the bioavailability of As and other elements from sikor and their impact on human health.

The authors of the study recommend that those responsible for public health, act to create awareness about the potential dangers of consuming baked clay in populations where this practice is prevalent.  As a result, the United Kingdom Food Standards Agency has advised pregnant women not to eat baked clay (http://www.food.gov.uk/news/newsarchive/2011/june/clay ).  However, public health officials in other parts of the world including Bangladesh, India, Africa and other parts of the world where geophagy is more prevalent need to also act urgently to advise women about the potential dangers of eating clay.

For further details, please contact Dr P.I. Haris, E-Mail: pharis@dmu.ac.uk

References:

Al-Rmalli, S.W.,  Jenkins, R.O., Watts, M.J., and Haris, P.I. Risk of human exposure to arsenic and other toxic elements from geophagy: trace element analysis of baked clay using inductively coupled plasma mass spectrometry.  Environmental Health 2010, 9:79 (23 December 2010).

http://www.ehjournal.net/content/9/1/79

Cascio, C., Raab, A.,  Jenkins, R.O., Feldmann, J. Meharg, A.A. and Haris, P.I. (2011)  The impact of a rice based diet on urinary arsenic.  J. Environ. Monit., 2011, 13, 257-265.

Related reports 

Food Standards Agency issues warning about eating clay.

http://www.food.gov.uk/news/newsarchive/2011/june/clay

Keep up to date

Submit Content

Members can keep in touch with their colleagues through short news and events articles of interest to the SEGH community.

Science in the News

Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

  • Fertilizer usage and cadmium in soils, crops and food 2018-06-23

    Abstract

    Phosphate fertilizers were first implicated by Schroeder and Balassa (Science 140(3568):819–820, 1963) for increasing the Cd concentration in cultivated soils and crops. This suggestion has become a part of the accepted paradigm on soil toxicity. Consequently, stringent fertilizer control programs to monitor Cd have been launched. Attempts to link Cd toxicity and fertilizers to chronic diseases, sometimes with good evidence, but mostly on less certain data are frequent. A re-assessment of this “accepted” paradigm is timely, given the larger body of data available today. The data show that both the input and output of Cd per hectare from fertilizers are negligibly small compared to the total amount of Cd/hectare usually present in the soil itself. Calculations based on current agricultural practices are used to show that it will take centuries to double the ambient soil Cd level, even after neglecting leaching and other removal effects. The concern of long-term agriculture should be the depletion of available phosphate fertilizers, rather than the negligible contamination of the soil by trace metals from fertilizer inputs. This conclusion is confirmed by showing that the claimed correlations between fertilizer input and Cd accumulation in crops are not robust. Alternative scenarios that explain the data are presented. Thus, soil acidulation on fertilizer loading and the effect of Mg, Zn and F ions contained in fertilizers are considered using recent \(\hbox {Cd}^{2+}\) , \(\hbox {Mg}^{2+}\) and \(\hbox {F}^-\) ion-association theories. The protective role of ions like Zn, Se, Fe is emphasized, and the question of Cd toxicity in the presence of other ions is considered. These help to clarify difficulties in the standard point of view. This analysis does not modify the accepted views on Cd contamination by airborne delivery, smoking, and industrial activity, or algal blooms caused by phosphates.

  • Effects of conversion of mangroves into gei wai ponds on accumulation, speciation and risk of heavy metals in intertidal sediments 2018-06-23

    Abstract

    Mangroves are often converted into gei wai ponds for aquaculture, but how such conversion affects the accumulation and behavior of heavy metals in sediments is not clear. The present study aims to quantify the concentration and speciation of heavy metals in sediments in different habitats, including gei wai pond, mangrove marsh dominated by Avicennia marina and bare mudflat, in a mangrove nature reserve in South China. The results showed that gei wai pond acidified the sediment and reduced its electronic conductivity and total organic carbon (TOC) when compared to A. marina marsh and mudflat. The concentrations of Cd, Cu, Zn and Pb at all sediment depths in gei wai pond were lower than the other habitats, indicating gei wai pond reduced the fertility and the ability to retain heavy metals in sediment. Gei wai pond sediment also had a lower heavy metal pollution problem according to multiple evaluation methods, including potential ecological risk coefficient, potential ecological risk index, geo-accumulation index, mean PEL quotients, pollution load index, mean ERM quotients and total toxic unit. Heavy metal speciation analysis showed that gei wai pond increased the transfer of the immobilized fraction of Cd and Cr to the mobilized one. According to the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis, the conversion of mangroves into gei wai pond reduced values of ([SEM] − [AVS])/f oc , and the role of TOC in alleviating heavy metal toxicity in sediment. This study demonstrated the conversion of mangrove marsh into gei wai pond not only reduced the ecological purification capacity on heavy metal contamination, but also enhanced the transfer of heavy metals from gei wai pond sediment to nearby habitats.

  • Cytotoxicity induced by the mixture components of nickel and poly aromatic hydrocarbons 2018-06-22

    Abstract

    Although particulate matter (PM) is composed of various chemicals, investigations regarding the toxicity that results from mixing the substances in PM are insufficient. In this study, the effects of low levels of three PAHs (benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene) on Ni toxicity were investigated to assess the combined effect of Ni–PAHs on the environment. We compared the difference in cell mortality and total glutathione (tGSH) reduction between single Ni and Ni–PAHs co-exposure using A549 (human alveolar carcinoma). In addition, we measured the change in Ni solubility in chloroform that was triggered by PAHs to confirm the existence of cation–π interactions between Ni and PAHs. In the single Ni exposure, the dose–response curve of cell mortality and tGSH reduction were very similar, indicating that cell death was mediated by the oxidative stress. However, 10 μM PAHs induced a depleted tGSH reduction compared to single Ni without a change in cell mortality. The solubility of Ni in chloroform was greatly enhanced by the addition of benz[a]anthracene, which demonstrates the cation–π interactions between Ni and PAHs. Ni–PAH complexes can change the toxicity mechanisms of Ni from oxidative stress to others due to the reduction of Ni2+ bioavailability and the accumulation of Ni–PAH complexes on cell membranes. The abundant PAHs contained in PM have strong potential to interact with metals, which can affect the toxicity of the metal. Therefore, the mixture toxicity and interactions between diverse metals and PAHs in PM should be investigated in the future.