By Adam CraigRhodes Serum Study Coordinator 2007/8Public Health Officer Trainee
The Rhodes Serum Dioxin Study's aim is to determine if there is a change in the serum dioxin levels of the Rhodes community relative to a control group (recruited from the Clarence Street Red Cross Blood Donation Centre) during the period of remediation of the Rhodes peninsula.
Blood samples have been collected from the Rhodes community and controls at baseline (before the remediation started in 2004/5) and at mid-point of remediation (in 2007). A third sample will be taken at the completion of remediation, envisaged to be in 2009. A description of the study methodology can be found in the Technical Report: Rhodes Serum Dioxin Study: Methodology and Baseline Data.
At baseline, 60 Rhodes residents and 594 controls provided blood samples for this study. Each of the Rhodes residents provided a 50ml sample while the controls provided a 5ml sample. At mid-point sample collection 52 (87%) of the Rhodes community group and 243 (41%) of the control group provided their second sample. Table 1 summarises the number of samples collected from each group at baseline and mid-point sample collections.
All samples have been stored at -20 degrees Celsius in specified freezers at the National Measurement Institute (NMI) in Pymble. In 2008 NMI extracted a portion of the samples of those participants who had given blood at both sample collection time points (52 Rhodes and 243 controls). These portions were combined into four pooled samples based on group and sample collection time points (2004 Rhodes, 2007 Rhodes, 2004 controls & 2007 controls) and were subsequently analysed by the Eurofins Analytik GmbH laboratory in Germany for the standard suite of dioxins and polychlorinated biphenyls (PCBs).
At baseline, Rhodes residents tended to be slightly older compared to the control group (mean age of Rhodes residents = 56; mean age of controls = 51.4). When excluding participants that have not provided mid-point samples (and hence have not been included in the analysis) the difference in mean age between the residents and control group reduces from 4.6 to 3.5 years. At baseline, controls were more likely to be regular smokers than Rhodes residents; this was reversed at mid-point sampling. Other comparison characteristics such as education levels, dietary intake of fish or dairy, and consumption of home grown vegetables or home reared meat/eggs tend to be similar between the groups (Table 1).
* Note: Figures for Controls at baseline differ to those in the Technical Report: Rhodes Serum Dioxin Study due to a corrected data coding error.
The full report of the dioxins analysis is included as Appendix 1.
Table 2, below, shows that between 2004 and 2007 blood serum dioxin levels have decreased for both residents and control groups. The concentration of dioxin-like chemicals in the pooled serum samples, expressed as 2,3,7,8-TCDD toxicity equivalent (TEQ) concentrations, decrease was greater in the control group than in the residents. However the decrease for TCDD, the key contaminant associated with the remediation site, was greater over the three year period in the residents compared to the controls.
WHO2005 TEQs presented here are calculated according to the lower bound procedure
The purpose of this mid point analysis was to identify if there has been a substantial exposure to clinically significant levels of dioxin associated with the remediation at Rhodes that would require immediate further investigation and/or public health action. The results indicate that the blood serum dioxin levels have decreased in both the residents and control group from 2004 to 2007 and thus any significant contribution to dioxin body burden in the local community from the remediation process is unlikely.
According to the criteria established for this study in 2004, these results do not warrant further investigation at this stage and a more comprehensive analysis will be undertaken at the end of the remediation period.