Miljøprojekt Nr. 1174 2007 – En registerundersøgelse af den danske befolkning – Hyppigheden af medfødte misdannelser i mandlige kønsorganer og forekomst af bryst-, blærehalskirtelog æggestokkræft blandt befolkningen med enkeltvandsforsyning

En registerundersøgelse af den danske befolkning

Summary

In Denmark approximately 70.000 households are supplied with drinking water from private wells without the same high standard quality control as the households supplied from public water supplies. In 2004 a random sample of 628 private wells revealed that 2 out of 3 wells exceeded the threshold value for pesticides, nitrate or bacteria and one in three exceeded the threshold values for pesticides. Pesticides were found in more than 60% of the private wells, and often more than one pesticide or degradation products were detected. Some pesticides have in previous studies been found to have endocrine disrupting abilities and have been related to increased risk of certain cancer types and congenital malformations in the male reproductive tract. Due to the unique population registers in Denmark, it is possible to link data on water supply with cancer and malformations registers. The purpose of this register study was therefore to study the relationship between water supply and hormone related cancers and malformations in the male reproductive tract and to validate the quality of these registers.

In this study data from seven population registers were used. The Danish Civil Registration System keeping a unique personal identification number (CPR number) for all citizens in Denmark and information about previous and current addresses. The Building and Housing Register (BBR) provided information about water supply for all addresses. Areal Information System (AIS) provided CPR numbers for the study population identified as all Danish people living in rural areas. The geological map from Geological Survey of Denmark and Greenland (GEUS) supplied a soil type to all addresses. The Danish Cancer Registry where information about breast cancer, ovarian cancer and prostate cancer were provided. The National Patient Registry and the Malformation Register keeps records of congenital malformations and operations for cryptorchidism and hypospadias (malformations in the male reproductive tract). In AIS the rural population in Denmark was defined and their CPR numbers recorded. These were linked to the health registers and CRP numbers of persons having one of the above defined diseases were identified in the rural population. In the Danish Civil Registration System the addresses of the rural population were identified and their water supply and soil type was recorded in respectively BBR and the geological map of GEUS.

In this partially ecologically study among all Danish people living in rural areas, women who were supplied with water from small private wells more often gave birth to a boy with cryptorchidism compared to women supplied from a public wells. No increased risk for hypospadias among sons of women with private water supply compared to public wells was found, but this is a rare malformation. Women and men who received water from private wells had no increased risk of respectively ovarian and breast cancer or prostate cancer. Women who lived in areas with clay soil more often experienced breast or ovarian cancer and gave birth to a boy with cryptorchidism compared to women living in areas with sandy soil. However, only the findings for breast cancer were statistically significant.

This study indicates that the population receiving water from private wells may be exposed to pesticides and metabolites that may affect their health which is in accordance with previous studies. The exposure to pesticides though drinking water is low compared to the exposure from the diet, but the types of pesticides found in the drinking water differ from those found in the diet. In addition, many pesticides and metabolites are found in drinking water extracted from surface near groundwater reservoirs.

This study is register based, and therefore does not include individually based information about exposures and possible confounders. It is therefore not possible to draw conclusions about any causal relationship between drinking water and health. It was for example not possible to take into account differences in social class and occupation between people with private and public water supply. In addition, problems with some of the registers were discovered which is discussed in more details in the report. This study can therefore only suggest a possible relationship between drinking water supply and health which needs to be confirmed in other studies with more appropriate designs. Since no firm conclusions can be drawn from this study it may be argued that it should never have been performed. However, one of the purposes of the study was to investigate the validity of the registers and discover problems with linkage which was done.