Report of field programme to investigate the relationship between selenium and iodine in the environment with iodine deficiency disorders in Sri Lanka, 12-26th February 1997. (WC/97/035R).
Abstract
This field visit is part of the DFID TDR project 'Prediction and Remediation of Human Selenium Imbalances (R6227)' the objectives of which are to:
1) Delineate risk areas in which Se toxicity or deficiency causes health disorders based on (a) mapping methodology for environmental selenium levels, (b) appraisal of environmental geochemical controls on the distribution of Se-responsive diseases, (c) database showing the role of Se in relation to human disease and epidemiology, and (d) an integrated GIS for human risk prediction.
2) Mitigate problems of natural Se imbalances by (designing and implementing land-use planning, crop and dietary Se supplementation methods .
The field programme described in this report was carried out as a collaborative exercise between the Department of Geology. University of Peradeniya, Kandy; Department of Environmental Sciences, Institute of Fundamental Studies (IFS), Kandy and the British Geological Survey (BGS, NERC, UK). Those participating in the field sampling programme are listed in Appendix A.
The fieldwork carried out in Sri Lanka follows three phases of field investigations in China to determine the links between environmental levels of Se and human Se deficiency and toxicity (diseases (Johnson et al, 1997; Fordyce et al, 1997; and Appleton et al, I 997). Unlike the situation in China, no data on selenium levels in the environment are currently available in Sri Lanka and the link between selenium deficiency and endemic disease has not been established. The occurrence of Iodine Deficiency Disorders (IDD) is widespread in Sri Lanka. It has recently been recognised that the selenoenzyme type I iodothyronine deiodinase (IDI) is responsible for the conversion of the prohormone thyroxine (T4) to the active hormone triiodothyronine (T3) which exerts a major influence on cellular differentiation, growth and development, especially in the foetus. neonate and child. Thus environmental Se status is likely to be an important factor in the aetiology of IDD. The objective of this study is to investigate the possible involvement of selenium deficiency in endemic IDD in Sri Lanka.
Endemic goitre is attributed mainly to iodine deficiency but other factors such as goitrogens, trace elements, and genetic factors have been implicated (Koutras, 1980). In Sri Lanka the simple explanation that iodine (deficiency leads to endemic goitre is open to much debate and for this reason other potential causative factors are actively being pursued. The Biochemistry Department, Faculty of Medicine, University Peradeniya is investigating goitrogens in the (liet (Prof. P A Perera pers. commun.) and Dr L Watawana (Department of Nuclear Medicine, University Peradeniya) considers there is strong evidence for a genetic link (Dr L. Watawana, pers. comm). Dissanayake and Chandrajith (1993) conclude that in Sri Lanka the role of I in endemic goitre is complicated with other trace elements such as Co, Mn, Se, F, As, Zn, Ca, Mg, Cu and Mo possibly being implicated in the aetiology of the disease.
The Field procedures adopted in Sri Lanka followed those developed in China during the initial phase of the project (Appleton, 1995; Johnson, 1995; Fordyce, 1996). The main objectives of the Field programme were to:
1) establish the relationship between the human Se status of communities (represented by hair samples) and their dietary Se intake (represented by grain and drinking water samples) to the local geochemical environment characterised by Se in cultivated soils.
2) relate the Se status of the population (represented by hair samples) and their dietary I intake (represented by grain and drinking water samples) to the local geochemical environment characterised by I in cultivated soils.
3) identify the effects if any, of environmental Se and I in the aetiology of IDD disease in Sri Lanka.
Fifteen villages were selected for the investigation based on previous studies and current investigations being carried out by the Medical Faculty of the University of Peradeniya. Five villages with high IDD incidence, five villages with moderate IDD incidence and five villages with low IDD incidence were chosen (Appendix 13). The work was scheduled to be completed within 2 weeks and this was taken into account when selecting villages.
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