Self reported health of people in an area contaminated by chromium waste: interview study

Multistage sampling

After piloting, 400 houses from each area were visited by trained interviewers using a multistage sampling procedure. Areas to survey were selected, and systematic sampling of every twentieth house was carried out. The person answering the door (if aged 16-74 years) was interviewed. If this person refused or there was no reply the interviewer moved on to the next eligible house, continuing in this way until the target number of questionnaires was completed. Only one person per house was interviewed. All interviews were carried out between 9 am and 5 pm and were completed in five days.

SF-36 health questionnaire

The SF-36 was used to measure self reported health. This comprises eight dimensions: vitality, general health, bodily pain, physical and social functioning, mental health, and role limitations due to physical and to emotional problems. After completion of the SF-36 all participants were asked about the difficulties they anticipated in moving from the area in which they lived, should they wish to do so. Additionally, residents of the contaminated area were asked whether they would attribute any such difficulties to the contamination, whether they believed that chromium was harmful to health, and how money allocated to the area should be spent. Age, gender, and housing tenure of the participants were recorded.

Statistical analysis and sample size

Means for each dimension were calculated for both groups and compared using unpaired t tests, after considering the distribution of the data. Multivariable regression analyses were then carried out to determine whether there were differences in SF-36 scores between the two groups after controlling for potential sociodemographic confounders. Similar analyses were then performed for the chromium group alone to examine further the effects of perceptions about harm from chromium and how money allocated should be spent.

Using published standard deviations for the SF-3617 a sample size of 800 (400 in each group) was chosen. This conferred a power of 80% with a two tailed significance level of 5% to detect a difference in health score of five points on the 100 point scale, which is considered to be clinically significant.18

Potential predictor variables

In univariable analyses of the two groups combined there is significant heterogeneity across age groups for all dimensions except role emotional, with health tending to decline with age (data not shown). Gender is only significantly associated with mental health and vitality, women showing poorer scores (data not shown). Table 2 shows the associations between each of three potential predictor variables and the eight dimensions of the SF-36. Owner occupiers had the best perceived health and those in rented accommodation generally the worst. Owner occupiers who believed that there would be a definite problem selling their house had lower health scores than those who believed that this was less likely and this was statistically significant for the dimensions of general, social and mental health, and role emotional.

Comparison of chromium and control groups

Table 3 shows the difference between the two groups for each dimension of the SF-36. In the univariable analysis there are small but statistically significant differences between the two groups for the dimensions of bodily pain, general and physical health, and vitality in the direction of better health in the control group. After adjustment for age and gender there was little change in the differences between the two groups but none of the differences was now significant. Further adjustment for the potential confounding of the other three factors measured in both groups resulted in little change, although for general health there was a statistically significant difference—again in the direction of better health in the control group.

Perception of health risk from chromium

Table 4 shows the scores on the SF-36 dimensions in the chromium group alone for those who believed chromium to be harmful and those who thought it was not harmful. Overall, 25% (98/398) of the chromium group believed that chromium was harmful. In the unadjusted analyses there were large and highly statistically significant differences in all dimensions of the SF-36, with those who believed chromium to be harmful having noticeably worse scores than either those who did not believe it was harmful or those (18/398) who did not know (data not shown). These differences persisted and remained highly significant after adjustment for the same sociodemographic variables as above. Overall, individuals who perceived chromium to be harmful to health scored on average at least 16 points lower on the relevant SF-36 dimensions than did those who thought otherwise.

Views on resource allocation

Participants in the chromium group were also asked how they would like money to be used if it were allocated to their area. Less than one third (121/383) favoured chromium remediation—removal or burial of the chromium waste—the remainder preferring expenditure on local amenities, housing, education, or employment. There are minor non-significant differences in adjusted scores between these two groups, ranging from −1.4 (95% confidence interval −10.4 to 7.6) to 2.6 (−3.0 to 8.3), and the direction of better health is heterogeneous. Adjustment for sociodemographic variables did not affect these results.

Study limitations

The drawbacks of this study include its cross sectional nature, which precludes verification of the direction of the associations. It is possible, although we believe unlikely, that chromium induced ill health causes individuals to correctly identify chromium as a health problem. Lack of objective validation of health status from medical records, the possibility of bias owing to awareness of the key hypotheses among participants, and the availability of only comparatively crude data on potential confounders—age groups and overall socioeconomic status of the two groups—may limit the robustness of the findings. As interviews were conducted during the day participants could have been unrepresentative in terms of employment and health status.

Health risks

Although chromium has known toxic effects, our findings are consistent with those from several previous negative investigations of the role of chromium on health in this population.12^–15 A more recent study on the health effects of living near to landfill sites in Europe showed an increased risk of congenital birth defects (odds ratio 1.63, 1.09 to 2.44) in Glasgow.19 In this study, however, it is likely that contamination of landfill included a wide range of toxins.

Risk perception and health

Despite the overall negative findings, the lower scores in participants who believe that chromium is harmful raises the possibility that knowledge of the history of land use may reduce generic quality of life in the absence of any documented adverse health effects. This points to the importance of perception in mediating reported health status. Other studies have raised similar issues. In one such study respondent “personality variables,” such as hypochondriasis, opinions about waste disposal, and environmental worry were associated with higher prevalences of physical and psychological symptoms. 20 21 Similarly, the Camelford incident, where the water supply in North Cornwall was contaminated by aluminium sulphate, suggested that the perception of normal and benign somatic symptoms may have been heightened by litigation, community action, self appointed experts, consumer opinion polls, media attention, and accusations of a conspiracy.22 The need for a prompt response, taking into account the importance of social and cultural factors, was underlined.22 Such factors include the nature of the public perception of risk. Risk is a social construct, and it is important in evaluating the threat from environmental hazards to introduce more public participation into both risk assessment and risk decision making.23 This makes the decision making process more democratic, improving the relevance and quality of scientific investigation and enhancing the legitimacy and public acceptance of the resulting decisions. In the current setting, a perceived lack of impartiality of investigations into chromium (G Watt, personal communication) highlights the importance of early public participation when evaluating health risks of environmental waste. An irony that underlines the complexity of this situation is that most of the chromium group preferred money to be spent in other areas governing quality of life rather than on chromium remediation.