|Endotoxins are components of the outer membrane of Gram-negative bacteria and are a biologically active component in most organic dusts. Occupational exposure occurs primarily in the agriculture industry and related sectors.
Endotoxin levels in air can be measured either in absolute terms (weight/m3) or as functional (bioactive) levels. The latter can be measured by use of the Limulus amebocyte lysate assay and levels are expressed as endotoxin units (EU)/m3.
Endotoxins that enter the upper respiratory tract are expelled by means of muco-ciliary transport. Smaller particles deposit in the deeper airways and are locally phagocytised by macrophages, a process that may result in inflammatory reactions. Therefore, systemic effects due to inhaled endotoxins are most likely induced by cytokines that are released from the lung into the blood.
Airborne endotoxin exposure has been shown to generate biological and clinical effects in man. The lung appears to be the main target organ and endotoxin ex-posure has been associated with decreased lung function in several experimental and epidemiological studies. Acute effects in humans after endotoxin inhalation are dry cough and shortness of breath accompanied by decreased lung function, fever reactions and malaise, and sometimes dyspnoea, headache and joint aches occurring a few hours after exposure. Chronic endotoxin exposure may lead to chronic bronchitis and reduced lung function.
Forced expiratory volume in 1 second (FEV1) is known to be the parameter most consistently affected by endotoxin exposure, and small decrements in FEV1 are early and sensitive indicators of respiratory impairment.
A clear exposure-effect relationship for the percentage change in FEV1 was found in healthy volunteers (pre-selected for being sensitive to endotoxin) ex-posed to endotoxins for 6 hours. The study indicated that 90 EU/m3 (9 ng/m3) is the highest level at which no acute across-shift change in FEV1 occurs. This result was combined with those from long-term studies. The extra decline in FEV1 after 40 years of exposure to 90 EU/m3 endotoxin was calculated to be up to 120 ml, which was considered as a non-adverse effect.
In conclusion, no adverse health effects are expected after chronic occupational exposure at 90 EU/m3.
Keywords: endotoxin, lipopolysaccharide, lung function, occupational exposure limit, respiratory effects, review, risk assessment, toxicity