Long-term health effects associated with working conditions in sewers

While carrying out their professional activity, sewer workers are exposed to many chemical and biological agents present in the air and/or water, by inhalation of gases, vapours or aerosols, by mucocutaneous contact and by ingestion.

In 2004, the INRS published the results of a study of mortality in Parisian sewer workers, conducted at the request of the City of Paris. It highlighted excess mortality, including a significant proportion by digestive diseases, cancers, and suicides.These results were borne out when the study was updated in 2009, leading ANSES to issue an internal request to assess the health risks specific to the profession of sewer worker and identify the causes of this excess mortality.

Workers exposed to numerous compounds

ANSES undertook an individual measurement campaign among the sewer workers of the City of Paris, between October 2014 and March 2015, in order to consolidate the very few data in the literature. These exploratory measurements showed that sewer workers are exposed to a cocktail of chemical and biological agents present in the water and air of the sewers. In general, the concentrations of pollutants in the air of the sewers are higher than the concentrations measured outside, due to the lack of air renewal and the confined space, and to the presence of sources of contamination specific to sewers.

This measurement campaign helped demonstrate exposure to carcinogenic, mutagenic and reprotoxic (CMR) compounds, and identify tasks entailing greater exposure than others, such as cleaning of the grit tank, high-pressure cleaning of screens or cleaning with machinery. In most situations however, the measured concentrations for each of the identified compounds are low compared to the reference values (Occupational Exposure Limits = OELs or Toxicity Reference Values = TRVs), which nevertheless does not guarantee the absence of any health effect associated with the particularly numerous co-exposures, the possible synergies between pollutants and the concentration peaks of certain pollutants.

Long-term health effects associated with the profession of sewer worker related to a multiplicity of risk factors 

With regard to the health effects, the symptoms most frequently reported by workers exposed to wastewater are digestive and respiratory symptoms, and irritation of the nose, throat and skin. An increase in the frequency of certain infectious diseases can also be observed, most of them being of limited duration and very rarely fatal.

The mortality studies indicate a significant excess mainly for liver and lung cancers, without it being possible to precisely identify one or more risk factor(s) responsible, in particular the chemical or biological agents to which the workers are exposed.

Lastly, the low status of the profession of sewer worker, the weakening of work collectives and the anxiety-provoking dimension of work in a sewer are all factors potentially associated with heightened distress at work.

ANSES’s recommendations

The Agency reiterates the general principles of prevention laid down by the French Labour Code, in particular giving priority to collective protective measures over personal protective measures.

In light of the conclusions of its expert appraisal, the Agency recommends gaining a better understanding of the chemical, microbiological and psycho-social risks, so that the necessary steps can be taken to protect the safety and health of sewer workers in the long-term.

It advocates optimising measures to reduce the exposure of workers to microbiological and chemical agents, by:

• developing mandatory vocational training for any person required to work in an underground sewer system; 
• paying particular attention to the tasks entailing the greatest exposure (optimising ventilation of the sewer system, mechanising these tasks, etc.);
• implementing hygiene measures and safety instructions in conjunction with the occupational health service;
• introducing mapping of the risks associated with the systems (identification, centralisation and updating of knowledge relating to the areas of the sewers where specific conditions apply).

The Agency considers it necessary to strengthen self-monitoring, check the compliance of non-domestic wastewater discharges with the discharge authorisations on a more regular basis, and encourage the establishment of systems whose flow conditions make self-cleaning possible.

ANSES also recommends providing increased medical supervision of the health of sewer workers, complying with the applicable opinions of the Technical Vaccination Committee of the French High Council for Public Health (HCSP) concerning leptospirosis and hepatitis A vaccination, and ensuring the traceability of exposure.

In terms of research, the Agency recommends continuing and implementing epidemiological studies for the monitoring of long-term health effects in sewer workers, assessing the effectiveness of the preventive measures that can be put in place, such as the mechanisation of certain tasks and organisational changes to work, continuing to measure individual exposure to pollutants,and studying the usefulness of developing research on biomarkers to improve the monitoring of multiple exposures of sewer workers.

Awareness campaigns should be organised, firstly to remind the general population that the sewer system is not intended for dumping just any kinds of waste, and secondly to clarify good disposal practices.

ANSES also stresses that the recommendations issued are part of a general context of climate change likely to have an impact on urban sanitation (change in the volume of water passing through the systems, temperature of the wastewater collected and transported, etc.). This impact in terms of prevention and protection of professionals required to work in sewer systems needs to be anticipated.