Introduction
The discourse on workplace hazards caused by dangerous substances often prioritises chemical agents, but the significance of biological agents is is frequently overlooked, despite their ubiquitous presence across various occupational settings. Long-term exposure to chemical agents in combination with potential pathogens is a challenging mix to tackle in sectors like healthcare, agriculture, cleaning, recycling, and many others. The intricate dynamics between these biological and chemical agents can exacerbate vulnerabilities to diseases and intensify chemical toxicity. Determining safe chemical thresholds and assessing biological agent virulence is particularly challenging, especially when they come together. Add to this the diversity of workers in terms of gender, age and health status, and it becomes even more difficult to set general occupational safety and health (OSH) standards for such combined exposures. Amidst this complexity, this article aims to present the current scientific consensus on combined exposure to biological and chemical agents at work and provide a clear overview of the intricate interplay between chemical and biological workplace hazards.
Definition and context
Definition
There is no commonly accepted definition of ‘combined exposure to biological and chemical agents’ but by analogy with ‘exposure to multiple chemicals’[1] it can be described as exposure to multiple chemicals and biological agents via single or multiple sources and/or pathways. Occupational exposure to a mixture of biological and chemical agents typically occurs in workplaces where the handling, processing, or disposal of biological materials necessitates the use of chemicals, increasing the complexity and potential health risks. The routes of exposure allow for a combination of exposure to all the agents via the skin, by inhalation or by ingestion.
Relevance in the workplace
Exposure to mixed biological and chemical agents in the workplace is a significant concern in OSH. Biological agents are present in many sectors and environments, and they can pose risks that are not always recognised due to their invisibility and/ or difficulty to predict where they occur and/ or quantify the exposure to them. Especially the risk of unintentional exposure to biological agents (such as in agricultural activities and waste management) is difficult to assess. When combined with chemical agents, omnipresent in most workplaces today, the potential occupational health risk can increase significantly. The uncertainties that are still associated with assessing the biological risk also complicate a proper risk assessment of chemical agents.
EU Legislation
Directive 2000/54/EC[2] on the protection of workers from risks related to exposure to biological agents at work defines ‘biological agents’ as ‘microorganisms, including those which have been genetically modified, cell cultures and human endoparasites, which may be able to provoke any infection, allergy or toxicity’. It is a specific directive that complements the general requirements set out in Directive 89/391/EEC[3], known as the OSH Framework Directive, and specifies requirements with regard to exposures related to biological agents. A wider definition of biological agents is sometimes being used: ‘biological agents’ are then microorganisms and other carriers of plant or animal origin that can cause adverse health effects in workers after exposure. In addition to living (micro)organisms (e.g. bacteria, viruses, fungi, yeasts and prions), substances or structures that originate from living or dead organisms (e.g. exotoxins, endotoxins, glucans, mycotoxins and allergens) are included[4].
The protection of workers from the risks of chemical agents is regulated by the Chemical Agents Directive (CAD - 98/24/EC)[5] and by the Carcinogens, Mutagens and Reprotoxic agents Directive (CMRD - Directive 2004/37/EC)[6] that sets out specific requirements for substances that may cause cancer, genetic mutation or reproductive toxicity in exposed individuals.
Similar to other OSH Directives, these three Directives emphasise the employer's obligation to carry out thorough risk assessments. Although the Directives do not explicitly mention the increased risk from combined exposure to biological and chemical agents, they place the responsibility on employers to consider all relevant factors. These factors include the type of work and work processes, the equipment and products used, the work environment, work organisation, individual vulnerabilities, etc. The Biological Agents Directive specifically highlights that risks must be assessed even when the presence of biological agents is unintentional. Moreover, the scope of the CAD extends beyond chemicals classified as hazardous according to the Classification, Labelling, and Packaging (CLP) Regulation (Regulation 1272/2008/EC[7]) to include process-generated substances. The CAD further stipulates that "in the case of activities involving exposure to several hazardous chemical agents, the risk shall be assessed on the basis of the risk presented by all such chemical agents in combination" (Article 4). Ultimately, it is the employer's duty to ensure that all specific conditions of the workplace are factored into the risk assessment.
Health risks from mixtures of Biological and Chemical Agents
Overview
Exposure to a mixture of biological and chemical agents refers to contact with a combination of living organisms (such as bacteria, viruses, or fungi) or of (dead) bacterial origin (such as endotoxins) and chemical substances (such as toxins, pollutants, or industrial chemicals). This exposure can occur in various contexts, including workplaces, natural environments, or even within our own bodies. The interaction between these biological and chemical components can have diverse effects on health, immunity, and overall well-being.
Chemical agents are found in almost all industrial and semi-industrial workplaces. Workers are typically exposed to biological agents where there is contact with natural or organic materials like soil, clay, plant materials (hay, straw, cotton, …), substances of animal origin (wool, hair, …), food, organic dust (flour, paper dust, animal dander), waste and wastewater, blood or other body fluids. More information on risks caused by biological agents can be found in the article on biological agents and in the EU-OSHA report Biological agents and work-related diseases: results of a literature review, expert survey and analysis of monitoring systems[4].
When different agents are combined, the impact on the worker can have a greater (synergetic) effect than what would be expected of the sum of the individual effects[8]. Certain pollutants (inhaled particulates but also polluted air contaminants absorbed through the skin) are known for weakening the immune system, meaning exposed workers can then become more susceptible to infections caused by biological agents. Combined exposure to airborne pollutants and microorganisms can affect respiratory health more dramatically when acting together. When certain chemicals weaken our immune systems, biological agents can cause more severe disease. Inhaled mixtures of gases, fine and ultrafine particles and volatile organic compounds, combined with the risk of biological agents, can be not only toxic but also infectious and even mutagenic or cytotoxic.
Furthermore, chemical agents can increase susceptibility to infection, or conversely, biological agents can weaken protection in healthy human cells, causing chemical agent toxicity to manifest itself at lower concentrations.
The identification of allergens and their differentiation from chemical agents is very challenging as the exact cause of the allergy at the agent level cannot easily be identified. For many occupations, the exact agent or substance causing the allergic reaction is not yet known.
Health effects arising from combined exposures
The human body depends on other living cells that are part of our healthy existence. For instance, the bacteria in our gut, or the bacteria and moulds on our skin, all of which help us to survive all external influences. It is called our microbiome, the collection of all living material in and around us[9]. As is known from studies on the impact of the microbiome, it can either help us detoxify certain chemical impacts or can turn rather harmless substances into more harmful ones[10]. In this sense, every exposure may be a combined exposure or the result of an interaction between chemical and biological factors.
For example, Streptococcus pneumoniae is a bacterium that has a complex relationship with its human host. Pneumococci are highly adapted commensals that primarily reside on the mucosal surfaces of the upper respiratory tract, facilitating transmission[11]. However, they can cause severe diseases when certain bacterial and host factors allow them to invade sterile sites like the middle ear, the lungs, the bloodstream, and the meninges. For instance, welders are at an increased risk of invasive pneumococcal disease that may be due to metal components in welding fumes acting as nutrients that enhance the adherence of pneumococci to lung tissue. In addition, inhalation of welding fumes can damage the lungs' immune defences. It is likely that both factors play a role[4].
The interaction between biological and chemical factors is inherently linked to either (human) health or disease. This interrelation plays a crucial role in our health, adaptation, and protection. The concept of the hologenome refers to the sum of our DNA and all the genomes or DNA of the microbiome surrounding us. Understanding the hologenome sheds light on intricate interactions between hosts and their microbiota, impacting fields such as occupational exposures and well-being[12]. Although this hologenome carries a vast amount of information in this genetic database, it is still not possible to predict health or disease by analysing DNA alone. A global carcinogenicity review, the ‘Halifax Project’, concluded:
“Our current understanding of the biology of cancer suggests that the cumulative effects of (non-carcinogenic) chemicals acting on different pathways that are relevant to cancer, and on a variety of cancer-relevant systems, organs, tissues and cells could conspire to produce carcinogenic synergies that will be overlooked using current risk assessment methods”[13].
Considering the complexity of exposures and, in addition, the reactions of living things to all kinds of exposures – termed exposome - reverses classical exposure science, where the precise measurement of single or few exposures is associated with specific health or environmental effects. A wide range of non-genetic factors in the environment in which we live and work, co-determine the likelihood and course of disease[14]. Thus, the exposome concept refers to the sum of all external exposures that have a significant combined effect on health from conception through life, from a variety of external and internal sources, such as chemical and biological agents, radiation and lifestyle factors. The concept of the exposome was introduced by cancer toxicologist Christopher Wild in 2005. He defined exposome as encompassing all life-course environmental exposures (including lifestyle factors), from the prenatal period onwards[15]. Exposome models reinforce the idea of a biography-to-biology transition, in that everyone's disease is the product of the individual history of exposures, superimposed on their underlying genetic susceptibilities[16]. The exposome is an integrated function of exposure on our body including what we eat and do, our experiences, and where we live and work. The chemical exposome is an important and integral part of the exposome concept. External stressors are reflected in internal biological perturbations; thus, exposures are not restricted to chemicals (toxicants) entering the body, but also include chemicals produced by biological and other natural processes in and around the body[17].
Traditional studies often focus on single factors, but the exposome considers the collective impact of multiple exposures, including genetic variations that may make some individuals more susceptible to certain conditions. In summary, the exposome is a holistic approach to understanding the complex interplay between our genetic makeup, our environment (including chemicals), and the myriads of microorganisms that live with us, shaping our health and susceptibility to diseases. It underscores the importance of considering the full spectrum of exposures in health assessments and disease prevention strategies[17].
The exposome concept, which includes all non-genetic risk factors experienced throughout a person's life, offers a more holistic approach to investigating how occupational exposures may eventually result in disease. In the framework of the EPHOR-project[18] the concept of the Working Life Exposome has been introduced. It can be described as ‘all occupational and related non-occupational exposures (e.g. lifestyle, behaviour) throughout the course of life’. The EPHOR- project brings together scientific partners from 12 different countries to develop a working-life exposome toolbox that will provide better knowledge on how the working life exposome relates to diseases. The project runs from 2020 to 2025. The working-life exposome concept may have significant effect in occupational health, as it helps to identify how workplace exposures affect workers’ health.
Difference in the concept of Occupational Exposure Limits (OELs) between biological and chemical agents
For many chemical agents, occupational exposure limits (OELs) have been set as regulatory limits on the amount or concentration of a substance in the workplace air[19]. The Chemical agents Directive 98/24/EC (CAD) defines an OEL as ‘the limit of the time-weighted average of the concentration of a chemical agent in the air within the breathing zone of a worker in relation to a specified reference period’[5] (usually an 8-hour workday). European legislation sets OELs for chemical agents in both the CAD and the CMRD.
OELs are based on health factors and are established by committees (e.g. the Risk Assessment Committee (RAC)) that review the available published and peer-reviewed literature from different scientific disciplines[19]. It should be noted that OELs assume exposure to a single chemical substance and do not take into account combined effects[20]. The ACGIH (American Conference of Governmental Industrial Hygienists) recommends that when substances have similar toxicological effects (i.e. similar toxicological effects on the same target organ/same mechanism of action), the combined effect should be considered as additive (the sum of the individual effects)[21] [20]. Based on this principle, OELs for mixtures can be calculated. However, this principle does not apply to more complex mixtures, i.e. to mixtures suspected of having a synergistic effect or to carcinogenic substances[20].
No OELs have been set for biological agents in EU legislation, although some EU Member States have set limit values for some toxins produced by biological agents. In principle it is possible to derive OELs for biological agents that have toxic or allergenic effects in the same way as for chemicals. However, the lack of good quantitative data on exposure and the associated effects hampers the derivation of OELs for biological agents.
For infectious biological agents, deriving an OEL is more difficult owing to a lack of knowledge about exposure and pathogenicity. It is therefore not very likely that OELs for biological agents that result in infectious diseases will be developed in the near future[4].
The essential difference between biological agents and hazardous chemical substances is their ability to reproduce. For some biological agents, a small amount of microorganism can grow considerably in a very short time under favourable conditions[22]. This is especially true for those biological agents that are occurring as an (uncontrolled) consequence of work processes.
Currently, quantification of infectious agents is based on cultivation and colony counting. However, this does not capture substances generated by organisms, fragments from dead organisms, or toxic or allergenic compounds. Alternative methods developed to identify these include (electron) microscope counting[4].
The temporal aspects of combined exposures
When assessing the risks of combined exposures, it is important to understand that the moment of exposure to the different agents may not occur at the same time. A worker may have been infected with hepatitis B and become a carrier, making him/her more susceptible to chemicals that can cause liver cancer later in life (e.g. exposure to vinyl chloride monomer)[23]. Although numerous associations between work-related factors and cancers are established, the effects of age and timing of exposure have only been studied to a limited extent [24].
Furthermore, it is important to consider both short-term and long-term effects. Short-term effects of acute exposure can lead to immediate health issues such as skin irritation, nausea, or respiratory distress. Synergistic effects are also possible: chemical agents may increase vulnerability to biological risks (e.g. metal fume exposure leading to invasive pneumococcal disease[25]) and vice versa (e.g. hepatitis B carriers becoming more susceptible to chemical agents).
Long-term effects typically result from chronic or repeated exposure over extended periods. These effects can be more subtle and may not manifest themselves until years or decades after the initial exposure, potentially leading to chronic health conditions such as cancer or chronic obstructive pulmonary disease (COPD).
Oxidative stress: the joint mode of action
All reactive oxygen molecules produced in excess within the cell as a result of normal cellular reactions need to be detoxified as quickly as possible, or the damage they have already caused needs to be repaired as quickly as possible[26]. All cells thus need to have their redox systems readily available to limit such damage of the reactive oxygen before (irreversible) damage will take place in lipids, proteins or DNA. One form of oxidative stress that can be linked to stress in lung tissue may be caused by inhaled particulate matter[1] (e.g. PM2.5). The presence of inflammatory cells, such as alveolar macrophages and airway epithelial cells, is associated with the occurrence of oxidative stress, when the respiratory system is under threat of external pollutants. After uptake into cells, PM2.5 tends to catalyse complex biochemical interactions, activate oxidases and metabolic enzymes, and cause mitochondrial dysfunction, which leads to reactive oxygen molecule overproduction that disturbs the intracellular working[27]. Oxidative stress has been extensively studied in (tobacco) smoke inhalation. It is a key contributor to both cancer and inflammatory diseases. The inflammatory response may generate further macromolecular damage. The induced damage may lead to functionally important genetic and epigenetic alterations [2]. In addition to PM2.5, exposure to both biological and chemical agents can further increase the oxidative pressure on our cells, making irreversible damage more likely to occur.
Risk assessment and mitigation
Risk assessment is the cornerstone of OSH management. Employers have the legal obligation to assess the risks to their workers' health and safety (see above). The risk assessment process involves systematically identifying and assessing risks, prioritising them, and implementing measures to eliminate or mitigate them.
For both chemical and biological agents, this involves identifying which substances workers are exposed to, in what form and quantity, and what the potential hazards are. This often involves measuring substances in the air and comparing the results with OELs (where available). Specific air sampling methods and standards are used for these measurements and expertise is required to establish an appropriate measurement strategy and to follow up and analyse the results effectively.
However, this approach does not sufficiently take into account the risks of multiple exposure routes and pathways, and the combined risk of exposure to chemical and biological substances (or even other non-chemical risk factors), including the possibility that such exposures may alter health effects or severity through interactive processes[28]. One approach to assess the risks of multiple exposures is the use of biomonitoring to measure exposures and effects at the worker level. Biomonitoring involves measurements of biomarkers in bodily fluids, such as blood or urine. However, measuring internal dose alone does not provide complete information about the potential health impact[28] and can lead to incomplete risk assessments and consequently less effective control strategies.
To address the complexities of multiple exposure scenarios, public health bodies have developed cumulative risk assessment frameworks. Cumulative risk assessment is defined as “an analysis, characterization, and possible quantification of the combined risks to health or the environment from multiple agents or stressors”[29]. For instance, the European Food Safety Authority (EFSA) uses this approach to evaluate the risks posed by multiple pesticide residues in food[30], while the US Environmental Protection Agency (EPA) applies it to assess environmental and social exposures on the health of the general population [31]. Although this method has been proposed for application in occupational settings[28] [29] [32] [33], its practical implementation in the workplace remains challenging due to a lack of knowledge, methodologies, guidance, and tools.
OSH practitioners should therefore apply the precautionary principle and use lower OELs for chemical agents (and biological agents, if available), based on measured exposure levels and the nature of the combined risk. For example, simultaneous exposures that result in greater-than-additive effects may warrant a lower action level compared to additive effects[29]. Additionally, it is practical to include multiple exposures in checklists and other tools, which traditionally focus on single, specific risks without considering interactive exposures[29] [32].
Health surveillance also plays an important role. Individual medical surveillance is essential not only to detect health problems at an early stage, but also to maintain a comprehensive overview of full work histories (including occupational exposures throughout the life course)[24] and to identify any personal factors that may affect work exposures.
To control and mitigate the combined risk of chemical and biological exposure in the workplace, prevention measures should be implemented in accordance with the hierarchy of prevention:
Examples from sectors facing combined biological and chemical exposure
In many sectors, workers may be exposed to both chemical and biological substances. For example, farmers may be exposed to chemicals such as pesticides, fertilisers and veterinary medicines, but also to biological agents such as bacteria, fungi and viruses transmitted by animals or parasites, and micro-organisms in organic dusts of grain or fine particles of air-dried spilled liquids. Other examples of sectors and occupations concerned include waste treatment and recycling, laboratories, healthcare, metal processing (metal working fluids), woodworking, and the energy sector. Below two examples are discussed.
Healthcare: the risks of surgical smoke
Surgical smoke is the airborne by-product that is generated by the use of energy-based instruments in the operating theatre[34]. In almost all (85%) surgical procedures, heat-producing devices are used in the patient's tissue for dissection or haemostasis (stopping bleeding). The use of high-speed mechanical devices and heat-producing devices produces a gaseous by-product called surgical smoke[35]. Examples of such surgical devices include lasers, electrosurgical devices, ultrasound devices, cauterisation devices and high-speed drills and cutters.
About 95% of surgical smoke consists of water vapour but the remaining 5% contains constituents that can be hazardous to health. These constituents include organic vapours, chemicals, cellular fragments, blood and tissue particles, viruses and bacteria, among others[35] [36] [37]. The composition of surgical smoke varies greatly depending on the technique and the energy-based instrument that is used, how it is used and the type of procedure applied[37] [38] [39]. Among the components that can be potentially harmful for human health are: biological agents (e.g. viruses), volatile organic components (VOC), polycyclic aromatic hydrocarbons (PAH), particulate matter (all sizes) and chemicals (ammonia, carbon monoxide, hydrogen cyanide/ sulphide). Benaim & Jaspers[37] have compiled a non-exhaustive list of the known components of surgical smoke, shown in the table below.
Table: The components of surgical smoke
| Component | Examples |
| Volatile organic compounds (VOC) | 1,3-butadiene, Acetonitrile, Acetaldehyde, Acrolein, Acrylonitrile, Allyl cyanide, Benzene, Benzaldehyde, Crotonaldehyde, Cyclohexanone, Ethylbenzene, Ethylene, Formaldehyde, Furfural, Methanol, Phenol, Styrene, Toluene |
| Polycyclic aromatic hydrocarbons (PAH) | Acenaphthene, Acenaphthylene, Anthracene, Benzo[a]anthracene, Benzo[b]fluoranthene, Benzo[k]fluoranthene, Chrysene, Fluorene, Naphthalene, Phenanthrene, Pyrene |
| Pathogens | Human papilloma virus, Human immunodeficiency virus, SARS-CoV-2, Hepatitis B virus, Serratia marcescens |
| Particulate matter | Coarse (PM10), Fine (PM2.5), Ultrafine (PM0.1) |
| Chemicals | Ammonia, Carbon monoxide, Hydrogen cyanide, Hydrogen sulfide |
Source [37]
The size of the particles produced depends on the energy device used. Electrocautery produces the smallest particles, while ultrasonic scalpels produce the largest ones[39] [40]. Other factors that affect the amount and size of particles are the energy level of the instrument used, and the characteristics of the tissue being processed. More smoke and smaller particles are produced during dissection and haemostasis of dense tissues such as liver, kidney and muscle tissues[40]. Particulate matter can be deposited in different parts of the respiratory system depending on its size. PM10 can reach the oropharynx[3] when inhaled. PM2.5 can penetrate the defences of the upper airways and reach the alveoli, causing respiratory tract irritation. PM0.1 can cross the alveolar-blood barrier and enter the bloodstream. PM2.5 has been shown to increase the risk of lung infections and lung cancer, and to aggravate and cause new heart and respiratory diseases[37] [39].
Bioaerosols (pathogens) may be produced in surgical smoke generated at low temperatures, for example when using harmonic scissors, and this smoke may contain live multidrug resistant Mycobacterium tuberculosis or viral DNA of hepatitis B virus, hepatitis C virus, HIV or human papillomavirus4. Based on the available scientific studies, it can be concluded that live viral and bacterial particles have the potential to persist in surgical smoke, but there is no high-level evidence confirming the infectious potential of surgical smoke[39].
Most studies indicate that the concentrations of volatile organic compounds (VOC) and polycyclic aromatic hydrocarbons (PAH) are lower than the available OELs but other studies have found concentrations above OELs[37] . For instance, Kocher et al.[41] conducted an experimental study and found concentrations of 1,3-butadiene, benzene and furfural, among others, well above the OEL. Moreover, since medical personnel are repeatedly exposed to a mixture of substances with varying toxicity, the health risk may be significant and cumulative, even at very low concentrations of individual substances[42]. Simultaneous exposure to particulates, PAHs and volatile organic compounds may also have synergistic and additive effects that have not yet been adequately identified[43].
The effects of the combined chemical and biological agents of surgical smoke on cells can be multifactorial (cellular, physiologic and immunologic): in lab animals, local cytotoxicity can lead to interstitial pneumonia, bronchiolitis, and emphysema.
Surgical smoke can cause a number of acute, dose-dependent health problems. Symptoms reported by operating room staff are headaches, eye and skin irritation, nausea, rhinitis and upper airway irritation and cough[37] [40]. More serious acute conditions such as asthma and pneumonia have also been associated with exposure[40][44]. Prolonged exposure has been linked to chronic lung diseases, including occupational asthma and chronic obstructive pulmonary disease (COPD). For example, a large US cohort study found that long-term employment in an operating theatre (>15 years) was associated with a 69% increased risk of COPD, compared with a 31% increased risk among those who never worked in an operating theatre[45]. Chronic exposure has also been linked to cardiovascular disease, pneumonia, chronic bronchiolitis, emphysema, pulmonary fibrosis and blood disorders such as anaemia and leukaemia. Although surgical smoke contains various chemical compounds, including some that have been identified as carcinogens, such as benzene, it's important to note that there is currently no conclusive scientific evidence linking exposure to electrosurgical smoke directly to the development of cancer. The potential long-term health effects of chronic exposure to the components of surgical smoke are an area of ongoing research[46].
To effectively manage the risks associated with surgical smoking, employers are required, under EU legislation, to assess the risks and implement prevention measures in accordance with the hierarchy of control measures.
The most effective preventive measure is to eliminate and/or reduce the risk e.g. by using surgical techniques that produce less smoke or less easily inhaled, larger particles, such as ultrasonic scalpels. The frequency of use of electrical equipment can also be reduced by adopting a conservative approach and technique to tissue dissection and haemostasis, thereby limiting the amount of smoke[40]. If it is not possible to avoid techniques that produce too much harmful smoke, point extraction can be used directly at the point where the smoke originates. Tanaka et al. (2023)[47] recommend using electric scalpels with built-in smoke evacuation to better regulate PM2.5 levels in the operating room. Additionally, the US Department of Occupational Safety and Health (OSHA) acknowledges the hazards associated with surgical smoke: they recommend utilising smoke evacuator hose nozzles positioned within a maximum distance of 5 cm or as close as feasible to the source of surgical smoke production[48].
In practice, proper ventilation still is an essential part of OSH management in the operating room. The conventional type of Heat Ventilation and Air Conditioning (HVAC) system is the Turbulent Mixed Airflow (TMA) and is considered adequate for non-specialised surgery (e.g. abdominal surgery). It is not recommended for specialised surgery (e.g. prosthetic implants, organ transplantation, complex surgical oncology, neurosurgery, cardiovascular surgery and surgery with long incision to closure time. Laminar airflow (LA) also called unidirectional airflow washes out contaminants form the clean zone. A hybrid ventilations system combines both TMA and LA. The temperature-controlled airflow (TCA) is a system that uses cooled air above the operating table that flows downwards due to the higher density of cooled air in a room that is 1.5°C warmer[49].
When smoke evacuation systems are not sufficient or during procedures known to generate high levels of smoke, personal protective equipment (respiratory protection) should be worn. It should be noted that a surgical mask is not considered respiratory protection[43]. While a surgical mask is a first line of defence against droplets, splashes and sprays, it does not provide a reliable level of protection against the inhalation of small airborne particles. A fit-tested filtering face piece respirator (FFP2; FFP3) protects the wearer against the risk of inhaling hazardous airborne particles.
It is also important to ensure comprehensive training for all operating theatre staff on the risks of surgical smoke and the proper use of smoke evacuation equipment and PPE. A survey among German operating theatre staff[50] (respondents: 359 surgeons and 142 operating room nurses) showed that only around 15% consider themselves as being well informed about the health hazards. Only one in two surgeons reported that they (mostly) pay attention to avoid surgical smoke during surgery. Reasons for not doing so included lack of awareness, time pressure, perception of low health risk and lack of adequate technology[50] .
Further information and references to national guidance documents are available on the website of the Surgical Smoke Coalition[44] and in the brochure of the European Specialist Nurses Organization (ESNO)[51].
Energy sector: Biomass Power Plants
Biomass is extracted from organic material such as wood and wood residues, crop residues and wastes from industry, agriculture, land management and households. Biomass is converted into solid, liquid or gaseous fuels that can be used to produce heat and/or electricity or as transport fuel (biofuels)[52][53].
Power plant processes can be divided into three groups: pre-combustion (handling, storage, fuel preparation), combustion (including flue gas treatment), and post-combustion (ash and by-product handling). Each of these 3 groups has its own inherent health and safety issues. Mixed chemical and biological exposure can occur especially during the pre-combustion phase[54].The main health risks to workers are related to endotoxins, actinobacteria and fungi. There is also mechanical irritation from contact with organic dust and chemical irritation from volatile organic compounds (VOCs) and particulate matter (PM) associated with diesel fuel combustion (emissions in the exhaust gases of trucks)[55] [56]. Biomass is increasingly being used to produce bioenergy, which means that more workers are exposed to biological and chemical agents associated with this activity.
Multiple exposures to these biological and chemical agents can have synergistic effects on workers' health, including the lower and upper respiratory tract, without immediately excluding other body systems. Workers highly exposed to biomass power plant emissions can suffer from toxic pneumonitis to severe chronic lung disease (asthma, chronic obstructive lung disease, allergic alveolitis).
Exposure to particulate matter comes from wood dust, raw or processed material (straw, wood, chips, pellets) in the forestry, wood pellet production, biomass generation/ laboratory. Wood (chips), when stored outdoors and especially when stirred up later in the process, can expose workers to micro-organisms, fungi and endotoxins and an organic dust component. Workers in the wood pellet industry, for example, can experience high concentrations of wood dust, with personal exposure measurements indicating levels that frequently exceed occupational exposure limits (OEL). In one study by Hagström (2008)[57], a third of the samples exceeded the Swedish OEL of 2 mg/m³ for inhalable dust. Wood dust has been recognised as an irritant, sensitiser, respiratory toxicant, and, for a limited number of species, a potential carcinogen. There have even been some cases of fatal carbon monoxide poisoning from the gas fumes in wood pellets storage rooms because of chemical degradation, even at room temperature[58] [59].
Exposure to bioaerosols of mixtures of fungi, bacteria end endotoxins, component of the PM (particulate matter) originating from wood chips, pellets, straw, grain, hay and organic waste. Research by Laitinen, S et al. (2016)[55] found microbial concentrations exceeding 10,000 colony-forming units per cubic meter (cfu/m³) during fuel unloading in biomass power plants posing a threat to workers’ health. Furthermore, high levels of bioaerosols were detected near ‘crusher and screen’ processes, with high concentrations of endotoxins (up to 130 endotoxins units per m−3) and fungi (up to 56,000 cfu m−3). The highest short-term inhalable dust concentrations were found when workers had to go to the screening and crushing department of solid recovered fuel-fuelled power plants: these were 1.5 times higher than the OEL15 min value for organic dust[55] . In general, exposure levels higher than 10,000 colony forming units per cubic metre of air are considered hazardous and specific fungal species such as Aspergillus fumigatus) require even lower thresholds. For endotoxins, which may be present in particles of a size below 1 µm, the occupational exposure levels of more than 90 endotoxins units per m³ are linked with adverse health effects when chronically exposed[60]. This level can be compared to 9 ng of E. coli lipopolysaccharides per cubic metre[61].
Exposure to volatile organic compounds (VOC) (e.g. aldehydes) originates from auto-oxidation of unsaturated fatty acids, off gassing from sawdust in the wood pellet production. The maximum level for total VOC has been set to 3,000 µg/m³ (Finnish Institute of Occupational Health)[62]. For a good indoor air quality, the target should be 10% of the above (300 µg/m³)[62]. Low levels of exposure to VOC such as terpenes contribute to gas-phase exposures, which, when inhaled, can cause respiratory inflammation. Hagström (2008)[57] found evidence of exposure to dehydroabietic acid, and exposure levels for resin acids approaching 74% of the British OEL for colophony, set at 50 µg/ m3. Although not a typical VOC as it is not volatile at room temperature, rosin (colophony) becomes volatile when heat is applied during the processing of wood (mainly pine). In addition to (allergic) skin complaints, it can also cause work-related asthma[57].
The most important measure to reduce worker exposure is to provide biomass power plants with good quality fuel (better microbial quality)[63] and ensure proper storage conditions to prevent microbial growth or chemical degradation during storage.
Other prevention measures include:
- automation of the installations, enclosure of conveyor belts, extraction hoods
- control rooms for the supervision of unloading fuel trucks, automated fuel sampling, and automatic cleaning systems
- minimising dust generation by implementing water-based dust suppression systems or other dust control measures. Also, good housekeeping practices in storage and processing areas can substantially reduce airborne particles
- implementing clear "black/white" zones to separate contaminated areas from clean ones. Signage and physical barriers should be used to designate these areas.
In addition, and if engineering controls are not sufficient to control the risk, appropriate PPE and occupational hygiene measures should be implemented:
- PPE: workers can be protected by respirators, protective gloves and protective clothing[55] .
- designated changing areas for work and street clothes, offering the possibility of frequent clothing changes to prevent cross-contamination.
- fully equipped shower facilities with adequate locker space, ensuring a clear separation between storage for work and street clothes.
Conclusions
In the workplace, workers often face combined exposures to multiple chemical and biological agents, which poses significant challenges for OSH management. One of the main concerns is uncertainty about the synergistic effects of multiple agents, where the interaction of several chemical or biological agents can potentially increase health risks beyond the effects of exposure to individual agents. The complex dynamics between these biological and chemical agents may increase disease vulnerability and enhance chemical toxicity. Little scientific research has been done on these effects, making it difficult to estimate the risks. This uncertainty requires a re-evaluation and adaptation of current OSH management practices. Traditional approaches that assess risks individually are inadequate to deal with the complexity of combined exposures. There is a need for comprehensive strategies based on cumulative risk assessment methods and monitoring strategies. Currently, OSH practitioners lack practical tools, such as an online interaction checker, that would allow them to explore possible interactions between exposures and carry out comprehensive risk assessments that take into account the cumulative impact of certain mixed exposures or conditions on the health of the workers. In addition, the development of the working life exposome toolbox through the EPHOR project can help to understand how multiple occupational exposures affect health and are associated with disease. It requires further elaboration to become a useful tool for workplace risk assessment, to support the identification of exposures and to identify effective preventive measures.
To manage risks effectively it remains important to, in accordance with the hierarchy of controls, focus as much as possible on eliminating risks at source, implementing engineering controls and raising awareness of health risks and safe working practices among employers and workers.
[1] Particulate Matter (PM): Tiny particles in the air, classified by size. PM10 (≤10 micrometres) includes dust and pollen. PM2.5 (≤2.5 micrometres) includes combustion particles. PM0.1 (≤0.1 micrometres) includes ultrafine particles from vehicle exhaust and industrial processes. These particles can penetrate the respiratory system and pose health risks.
[2] Epigenetic alterations are changes in gene expression that do not involve alterations to the underlying DNA sequence. These changes can be influenced by various factors, including environmental conditions, lifestyle, and even experiences.
[3] The middle part of the throat, behind the mouth. The oropharynx includes the soft palate (the back muscular part of the roof of the mouth), the side and back walls of the throat, the tonsils, and the back one-third of the tongue.
