Animal farms includes dairy farms, cattle farms, swine farms, concentrated feeding operations (CAFOs), etc. Over the past two decades, there is a growing trend of shifting from small scale family owned farms to large scale animal farms in both North America and globally.1 With the expansion of livestock production, there are also increasing concerns about the environment impact of agricultural production. One of such concerns is the impact of exposure to endotoxin to agricultural workers’ occupational health, especially respiratory health.
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Endotoxin is lipopolysaccharides that are part of the outer membrane of Gram negative bacteria. Workers in animal farms are exposed while working since there are high levels of endotoxin in animal fecal waste. According to the Bureau of Labor Statistics, there are 856,300 agricultural workers in US in 2016.2 And there is an even larger population of animal farm workers globally who are working in similar conditions. Therefore, endotoxin exposure in animal farms is a global occupational health issue. There are multiple stakeholders at play around this issue, including animal farm workers, farm owners and regulatory agencies.
Animal farm workers are the ones at risk of being exposed to endotoxin and potentially suffering from both long-term and short-term health effects. However, many of the workers may not seek out resources and advocate for their own rights and health in fear of losing their jobs and income. Additionally, 27% of farm and 29% of animal slaughterhouse workers are undocumented immigrants, while only 5% of the general US workforce is made up of undocumented immigrants.3 These workers face additional challenges, such as language barriers and fear of deportation, if they try to advocate for their occupational health. Animal farm owners are mainly concerned with making maximum profit, and are not likely willing to implement waste treatment and management technologies in order to keep the cost as low as possible unless they are legally required to. This is why regulatory agencies, such as Occupational Safety and Health Administration (OSHA), need to step in to establish regulatory standards and guideline for endotoxin levels, and help protect the health of the large population of animal farm workers.
The source of containment is endotoxin is mainly present in the fecal waste from the animals. The primary route of exposure to exposure for workers is through the inhalation of airborne particles.4 Since this is an occupational exposure, the exposure depends to the type of tasks workers are performing and how long workers spend on different type of tasks. For workers who spend more time on shift performing tasks that involves more direct interaction with animal and closer interaction with fecal waste (for example, workers cleaning up animal facilities or transporting animal waste), they are more exposed compared to workers who spend less time and have more indirect interaction with animals and their fecal wastes. Toxicology: Exposure to endotoxin is related to respiratory diseases in animal farm workers, including both short term health effects such as chest tightness and inflammation, and chronic health effects such as chronic bronchitis and chronic obstructive pulmonary disease (COPD).5 In order to set effective standards and regulation on endotoxin in an occupational setting, it is important to establish a dose response relationship for the inhalation of endotoxin.
In a controlled human exposure study (Michel, 1997), subjects were give endotoxin’s purified derivative, lipopolysaccharide (LPS) at doses of 0.5, 5, and 50 ?µg (as well as saline for control) through inhalation.6 The inhalation of given doses of LPS produces inflammatory responses, at both systemic and bronchial levels. The inflammatory responses are evaluated by clinical symptoms, fever, FEV1, blood polymorphonuclear neutrophils (PMNs) and both the blood and the urine concentrations of the C-reactive protein (CRP). Researchers found a significant increase in CRP and PMN levels after the administration of doses as low as 0.5 ??g of inhaled LPS healthy subjects. PMN and CRP level changes are indicative of a more acute immune response than clinical symptoms or lung function (FEV1) changes. This suggests that the no-response threshold is potentially lower than 0.5 ??g. (0.5 ??g corresponds to exposure less than 50 ng/m3 airborne LPS for a 10hr period.) Epidemiology: To evaluate the exposure risks animal farm worker are experiencing, a few cross-sectional studies have been conducted in dairy farm workers, swine farm workers, etc. One cross-sectional study looked at the occupational exposure of endotoxin in workers from 13 California dairies farms.7 The mean personal exposure to endotoxin among 225 workers is found to be 453 EU/m3. EU stands for endotoxin unit, which is a measure of endotoxin activity. One EU is equal to 0.1 to 0.2 ng of endotoxin.8 The study also found that reported endotoxin concentration from ambient area sample are much lower than personal exposure concentrations at the same dairies. This provides important insight for regulatory agencies about how to monitor and regulate occupational exposure risk.
The study also found that workers who has the highest personal exposure are workers who spent the longest time on the re-bedding of freestall barns. This also shows endotoxin exposure could vary from task to task, and depends on how much time workers spend on each task. Another cross-sectional study compared the exposure levels of 205 dairy workers to 45 vegetable processing workers (control group) in large scale California Dairies.9 In this study, researchers found that the average personal exposure was 329 EU/m3. This study also looked at the lung function and observed an acute decrease in forced vital capacity (FVC) by 22mL per hour worked. FVC is the amount of air that can be exhaled out after taking the deepest breath possible measured by a spirometer, and is a reflection of lung function. Cross-sectional studies are useful for helping to understand the exposure risk throughout a large population of animal farm workers, as well as observing the acute respiratory health effects. However, even though there is a control group of vegetable workers, there are still potentially many variations between the different dairy farms, which makes it difficult to interpret the reported associations between exposure to endotoxin and decrease in lung function. Also, it is difficult to infer about long term health effects from cross-sectional studies.
In addition to cross-sectional studies to measure the short-term health effects due to occupational exposure to endotoxin, cohort studies are also conducted to investigate the long-term respiratory health effects of endotoxin exposure. In one study conducted in the Netherlands, researchers closely followed 171 pig farm workers over the course of 3 years.10 Researches found by personal monitoring of these pig farm workers that the average long-term exposure to endotoxin was 105 ng/m3 (1050 EU/m3). Researchers also observed an annual decline of 73 ml/year in FEV1 and 55 ml/year in FVC, both of which are measurements of lung function. Researchers also significant association between the endotoxin exposure and the decline in FEV1 and FVC after adjusting for factors such as smoking patterns, age, and baseline levels for FEV1 and FVC. Compared to an annual decline of 29 ml/year in FEV1 in the greater population due to age, 73 ml/year is rather a significant decrease of lung function in animal farm workers.11 Therefore, endotoxin exposure has a long term negative impact on the respiratory health of animal farm workers, in addition to the acute health effects shown in cross-sectional studies.
From the analysis of toxicology and epidemiology studies, endotoxin is shown to have a negative impact on the respiratory health among animal farm workers, constituting a significant issue in occupational health. The high level of exposure to endotoxin in current working conditions for animal farm workers has been shown to trigger acute inflammatory responses in human subjects, and lead to decline in lung function over both short and long periods. Such high, unhealthy endotoxin levels may be partially due to current lack of regulation in US. Currently, there are no established occupational exposure limits (OELs) in the United States. There is a recommended OEL of 50 EU/m3 proposed and a temporary legal limit of 200 EU/m3 over a 8 hour shift in the Netherlands.
Despite the lack of regulation in the Unites States, some animal farms have adopted alternative waste management and treatment technologies, which studies have shown are helpful at decreasing endotoxin levels. In one study conducted in North Carolina, researchers compared area sampling results of endotoxin concentrations between two swine farms using conventional lagoon-sprayfield technology and fifteen other swine farms that used alternative management systems for animal waste treatment. They found that five farms using alternative technologies, such as solids separation-filtramat separator and automated windrow composter, have significantly lower endotoxin levels compared to farms using traditional methods. Therefore, introducing and recommending alternative waste treatment technologies to animal farms would help mitigate this occupational health issue, despite the current lack of regulatory standards for endotoxin in the US. Recommendations and conclusions: In order to mitigate this occupational health issue, setting regulations for occupational exposure levels in livestock farm is necessary. However, in order to establish to regulatory standards, more research needs to be done on minimizing the variation between different studies. One study in 2015 found that there is significant variation among the results of endotoxin levels of the same samples measured by different laboratories.14 The differences could be contributed to variation in sample collection (filter type, sampling procedure), sample analysis (extraction temperature, extraction solvents, assay type, endotoxin standards) and differences in reporting units (EU, ng). The Netherlands OELs are measure using the European occupational standard sampling procedures by the European Committee for Standardization, but they have not been adopted by the United States for endotoxin sampling. Therefore, standardization between different labs needs to be established before comparing different study results and proposing appropriate occupational exposure limits.
Also, there is currently little communication to the animal farm workers about the risk of endotoxin exposure that could be found. In additional to setting up regulatory standards, it also important to develop educational material that provides information and resources for workers to learn more about the endotoxin’s health hazard and ways to minimize exposure during work and brining exposure back home. In conclusion, currently a large population of animal farm workers are exposed to high levels of endotoxin, which have shown to have negative impact on their respiratory health, both acutely and chronically. Setting occupational exposure limits for endotoxin in animal farms is recommended. Further research is needed to standardize different laboratory methods for measuring endotoxin levels in order to compare previous study results, and more studies are also needed to develop standard sampling procedure for regulating occupational endotoxin exposure. Additionally, education resources and information about endotoxin, its health hazard and how to minimize exposure, should also be provided to workers.
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