New Mortality Study: Results Do Not Indicate Overall Excess Mortality Among Residents Living Near the Lacq Industrial Basin

The purpose of the mortality study was to assess potential excess mortality among residents of the Lacq area compared to the general population of Aquitaine. This study relied on two analytical methods:

• An initial raw analysis strategy covered the period 1968–2014. It consolidated the results of the 2001 study, which covered the period 1968–1998 (98 municipalities divided into an exposed residential zone and two comparison zones less exposed to industrial emissions from the Lacq basin)

• The second strategy took into account knowledge acquired over time, particularly the 2007 and 2016 area-specific risk assessment studies, and was based on measurements of pollution sources and a modeling of pollutant emissions at the Lacq site. This allowed for a refined classification of the study area into three zones comprising 99 municipalities: a zone comprising the residential municipalities most exposed to industrial emissions, an intermediate exposure zone (moderately exposed), and a zone with little or no exposure. For this more recent period (1999 to 2014), potential confounding factors such as the socioeconomic status of populations—which can introduce bias due to its established link with mortality—were also taken into account at the aggregate municipal level.

Regardless of the analytical method used, the results did not reveal an excess risk of death for all causes of death, all cancer deaths, deaths from respiratory cancers, deaths from lymphoid tissue cancers, or deaths from digestive cancers in the areas of residence closest to the sources.

Furthermore, the second analysis method revealed a significant under-mortality for all cancers in the most exposed area.

According to both methods, the analyses extended to 2014 did not confirm the excess mortality for all causes of death combined and all cancers among those under 65 observed in the 2001 study.

Nevertheless, questions remain regarding respiratory and circulatory diseases

When considering the risk of death by specific cause, excesses were observed primarily for non-cancerous respiratory and circulatory diseases, even after accounting for certain confounding factors. These excess deaths are not correlated with the distance between the place of residence and the Lacq industrial area. Furthermore, this study, based on data aggregated at the municipal level, does not account for individual data that may be linked to the onset of certain conditions (hereditary,
behavioral, occupational factors, mobility, lifestyle habits, etc.).

Thus, these results raise hypotheses regarding differences in risk by residential area. Occupational exposures, residents’ mobility, and healthcare utilization must be taken into account in the participatory health survey to allow for a better understanding of these results.

The morbidity survey in the Lacq area will also explore the two health indicators related to respiratory and circulatory diseases.

Launch of the analysis phase of the morbidity study in the Lacq area

In parallel with the mortality study, Santé publique France has initially launched an exploratory morbidity study.

The objective of this exploratory study is to assess the feasibility of a morbidity study among the resident population of the Lacq industrial basin and, in particular, to identify the conditions of interest and the data sources necessary for their analysis.

The conditions of interest to be included in the morbidity study were identified following the completion of:

• a review of the literature on morbidity and mortality studies of chemical, petrochemical, or mixed industrial sites;

• a toxicological analysis of the 9 substances of interest identified during a prior quantitative assessment of health risks in the area.

The selection of conditions was prioritized following a qualitative study with local stakeholders and a study measuring local healthcare professionals’ perception of increased risk for the various conditions. For each condition of interest selected, the available indicators were identified, along with their spatial and temporal scope and their limitations (reliability, required statistical power).

The indicators thus pre-selected are respiratory and cardiovascular diseases and diabetes. Acute and chronic respiratory conditions in adults and children, including asthma, can be studied using indicators from the national health data system (hospitalizations, drug reimbursements), as well as certain cardiovascular conditions and treated diabetes. Perinatal morbidity will be studied provided there are sufficient case numbers. In the absence of indicators or registries, digestive and nervous system disorders, as well as cancers in adults, cannot be studied. The next step based on these results is the development of a detailed protocol for studying morbidity in the area, which will be developed in consultation with a committee of experts. It will describe the analysis strategy for each of the selected conditions.

Once the protocol is finalized, the analysis phase for the identified conditions will begin. The results of this upcoming study will enable the exploration of a health indicator for this area and, more generally, the evaluation of the utility of medical-administrative databases in the absence of a registry for studying health impacts in investigations of contaminated sites and soils.