The Evidence For Causal Association Between Exposure To Depleted Uranium And Malignancies Among Children In Basrah By Applying Epidemiological Criteria Of Causality

 

 

 

 

 

 

 

 

Alim Yacoub*,     Imad Al- Sadoon**    & Janan Hasan***

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

* Alim Yacoub, MBChB, DPH, MSc, PhD, MFCM

Dean and Professor, College of Medicine, Al- Mustansiriya University

 

 

** Imad Al- Sadoon, MRCP, Dean and Professor, Basrah Medical College

 

 

*** Janan Hasan FICN Assistant Professor, Basrah Medical College

 

 

 

key Word  :  Depleted Uranium , Malignancies  Criteria Of

 

 

 

Abstract                                  

 

Criteria for assessing causal association in observational studies (as described by Hill) have been applied to examine the association between exposure to depleted uranium and the rising incidence of malignancies (specifically leukaemias) among children in Basrah, southern Iraq following      the 1991 military aggression on Iraq. These criteria include time sequence, dose - response relationship and consonance with existing knowledge.

 The rise in the incidence rate of malignancies among children have been found to be noticeable from 1995 onwards (7.8/100000 in 1995, 10.7/100000 in 1999 and 13/100000 compared to only 3.98/100000 in 1990). Such trend fulfills time sequence criterion whereby the outcome follows a latency period of     almost 4 years following exposure to depleted uranium. Examination of the geographical distribution of such malignancies in Basrah over the period from 1993 to 2000 reveals that areas to the west of Basrah city (where levels of contamination of soil, plants and water with D.U are higher) have higher incidence of malignancies compared to areas east or south east. This finding fulfills dose-response criterion. The shift of the incidence of leukaemias in recent years towards younger children (below 5 years of age) supports the criteria of biological plausibility, specificity and consistency with findings from other parts of the world which have been exposed to ionizing radiation .

 

Introduction                                  

 

The rise in the incidence rate of malignancies (specifically leukaemias) among children below fifteen years of age in Basrah following the 1991 military aggression on Iraq has been  well-documented 1,2  .

There is circumstantial evidence that such rise is due to continued exposure to depleted uranium which has been used by the western allies in their aggression. However such evidence need to be supported by applying more rigorous scientific methodology. Sir Bradford Hill postulated what has been called criteria of causality to establish the causal association between two variables in observational studies3. These criteria include  time sequence , dose response relationship, consistency , specificity and biological plausibility or consonance with existing knowledge  .

In this paper we report  the results of applying such criteria to  data which has been gathered on the incidence of malignancies among children in Basrah for the period 1990 to 2000 to examine its association with exposure to depleted uranium .

 

Methodology

 

It has already been mentioned earlier that a cancer registration system has been set up in the main maternity and children hospital in Basrah governorate, southern Iraq where information on all admited, malignant cases among children bellow 15 years, of are recorded and analysed by authors 1. It has already been mentioned that this hospital serves as the main referral centre for the management of malignancies among children in the area. Information on the incidence is updated every year and the the following indicators are calculated :

1- Annual incidence rate of malignancies per 100000 of children below 15 years of age. This is worked out by relating the registered numbers of malignancies  to estimated population  of children for that year

2- Percentage rise in the incidence of malignancies in general and leukaemias in particular for each year compared to the incidence in 1990 . This is calculated by the following formula:

Percentage rise in a given year =

 

 


                             3. The spatial distribution of malignancies in Basrah by working out the annual incidece rate for each district of Basrah for the periods 1993 – 1998, 1999 and 2000 .

4- The proportion of  children below 5 years of age with leukaemias out of total children affected  for the period  from 1990 to 2000 .

 

 

 

 

 

 

 

Results

 

The results of the study relevant to each criterion of causality are presented below .

 

A- Time sequence relationship                                                                   .

 

Table 1 presents the incidence of different types of malignancies among children in Basrah during the period from 1990 to 2000 . It can be clearly seen that a noticeable rise in total malignant is observed form 1995 onwards ( 38 in 1995 , 65 in 1999 and 92 in 2000 ) compared to only 19 cases in 1990 . The corresponding figures for leukaemias  only are 25 in 1995 , 30 in 1999 and 60 in 2000 compared to 19 cases in 1990 .

The percentage rise in the in incidence of all  malignant diseases and  in the incidence of leukaemias are shown in fig 1 . It can be clearly seen that such rise started from 1995 onwards . The percentage rise in all malignancies compared to 1990 are 121% , 242% and 384%  in 1998 , 1999 and 2000 respectively . The corresponding rise figures for leukaemias are 60% , 100% , and 300 % for the same years.

 

B- Strength of  association

 

The  annual rates of malignancies among children in Basrah from 1990 to 2000 are shown in table –2 .The substantial rise in such incidence rates over the years is clearly demonstrated .The  risks  in 1995 , 1996 and 1999 are almost doubled  compared to1990 . In 1999 it is almost 3 times higher and in 2000 it is four times higher compared to 1999 .

 

C- Biological plausibility and consonance with existing knowledge  

 

Table –3 show the proportions of children below 5 years of age with leukaemias

out of total children below 15 years of age during the period 1990          to 2000 . The shift  towards younger age group can  be clearly observed .More than half of cases ( 57% ) are below 5 years of age in 2000 compared  to 13% in 1990  .  Such shift  confirms   early  exposure of young

 

 

population to radiation with succeeding years. It is well known that the risk of  cancer among younger population exposed to radiation is higher .

 

D-Dose – response relationship                                                                 .

  

This criterion can be clearly ascertained by examining the geographical variation in the incidence rates of malignancies among children in Basrah over the period from 1990 to 2000.Table-4 demonstrates such distribution .

   It can be seen that areas where higher level of background radiation was measured ( such as Al-Zubeir west of Basrah city and Al-Hartha , north of the City ) have higher incidence rates . Such rates are noticeable in 1999 and 2000 .

 

Discussion                                                                                   

 

The demonstration of the causal association between cancer and a risk factor has always been based on epidemiological evidence. Application of Hill’s criteria of causality has provided strong evidence for causal association between lung cancer and smoking or mortality due to cardiovascular disease among British doctors in relation to smoking 4 .

In this study the circumstantial evidence provided earlier on the relation between rising incidence of cancer among children in Basrah and exposure to depleted uranium 1,2 is further supported by the application of Hill’s criteria of causality . Time sequence relationship criterion is fulfilled by the noticeable rise in such incidence of leukaemias  starting from 1995 i.e. almost after 4 years of exposure to ionising radiation, a period equivalent to the latency period of this type of malignancy . Strength of association is demonstrated by the sustained rise in the risks of occurrence of malignancies among children in Basrah over  the last 10 years. This reflects the results of cumulative exposure to radiation among the local population .

Earlier measurements of background radioactivity  of soil , plant and water samples taken from different areas of Basrah5 showed that areas west of Basrah  had higher level of background radioactivity compared to eastern areas.

The results of the spatial distribution in Basrah of malignancies is consistent with the finding fulfilling dose – response criterion i.e. areas with higher level of  exposure had higher level of cancer among children. The shift of incidence of leukaemias towards younger children is consistent with findings from other studies about childhood leukaemias among people living  in the vicinity of nuclear reactors 6,7 .Thus the criteria of consistency and biological plausibility are  fulfilled .

In conclusion, the evidence provided in this paper further supports            the circumstantial evidence  described earlier about the causal association between exposure to depleted uranium and the incidence of malignancies among children in Basrah , southern Iraq

 

 

References                                                                                  .

 

1.   Yacoub, A. , Al-Sadoon  I, Hasan G. etal. Depleted uranium and health of people in Basrah : epidemidogical perspective . I. Incidence and pattern of malignent cases among children in Basrah . The Medical Journal of Basrah University 1999; 17:17-25

2.       Yacoub, A.,Al-Sadoon I. Hasan G. Further evidence on the relation between depleted uranium and the incidence of malignancies ( with specific reference to leukaemias ) among children in Basrah , southern Iraq . The Medical Journal of Basrah University 2000 ; 18:3-6

3.   Hill B. The environment and Disease: association or causation . Proceedings of The Royal Society of Medicine 1965; 58:295 – 300 .

4.       Doll R. & Hill B. Mortality of British doctors in relation to smoking  National Cancer Institute Monograph 19 . Editor : W. Haenzel , 1966 .

5.   سعـاد العزاوي ، بهاء الدين معروف ، مقدام محمود صالح ، وآخرين ، التلوث بالراديوم 266 الناجم عن استخدام القذائف الحاوية على اليورانيوم المنضب في المنطقة الجنوبية من العراق . اعمال الندوة العلمية الدولية حول استخدام الأسلحة المحرمة وتأثيراتها على الأنسان والبيئة في العراق . مركز ام المعارك للبحوث والمعلومات بغداد 2000

6.   Taylor DM & Taylor SK. Environmental Uranium & Human Health, Reviews of Environmental Health  1997;12:147-253

7.   McLaughlin JR. , King WD , Anderson etal . Paternal radiation exposure and leukaemia in offsprings. British Medical Journal 1993;307:959-966 .

 

Table  1

Incidence of malignant disease among children in Basrah
 

Table 2

Incidence rate of malignant diseases among children in Basrah from 1993-2000 compared to 1990.