Individual exposures to particulate matter and endotoxin in dairies have increased as operations have transitioned to larger herd sizes. A cross-sectional study at 13 California dairies and one non-dairy control facility was conducted to determine associations between endotoxin concentrations measured in fine particulate matter (PM 2.5) and respiratory function in these workers. Previous research found that dairy work was associated with acute airway obstruction in comparison to controls. While endotoxin levels in PM 2.5 have been previously reported, their effects on lung function have not been studied among California dairy workers. This paper also examined correlations with PM 2.5 concentration, inhalable particulate matter (IPM), and endotoxin in IPM. Personal samples collected from a total of 185 dairy workers and 45 control workers were included in the analyses. Findings showed that dairy facilities had higher (p < 0.001) endotoxin in PM 2.5 when compared with the control facility (3.3 EU/m 3, 0.6 EU/m 3, respectively). Endotoxin in PM 2.5 was weakly correlated with PM 2.5 concentration (r 2 = 0.16, p < 0.05) and IPM endotoxin (r 2 = 0.35, p < 0.01), but not with IPM concentration. When controlling for age, ethnicity, smoking, height and personal protective equipment use, PM 2.5 endotoxin exposure was associated with lower crossshift in forced expiratory volume in 1 second (FEV 1) and forced vital capacity (FVC) only among taller workers (p = 0.006). This is the first study to present personal occupational exposures to endotoxin in PM 2.5 measured on Californian dairies. Despite lower levels than in other industries, such as poultry farms, this study suggests that some workers may be affected, and efforts should be aimed at mitigating pollutants in order to maintain endotoxin concentrations below recommended levels.
As food sources have changed with industrialization and population growth, small farms are being replaced by large-scale operations that offer lower cost and higher productivity [
Chronic exposure to organic PM can lead to decreased lung function, chronic bronchitis, byssinosis, asthma, and chronic obstructive pulmonary disease (COPD) [
This study focused on the potential occupational risks of exposure to PM2.5 endotoxin on California dairies. Endotoxin, also known as lipopolysaccharide (LPS) complex, is a heat stable, toxic molecule originating from the cell membrane of gram-negative bacteria. LPS is made up of a lipid A portion, core, and O-antigen. The lipid A portion of the LPS complex is responsible for its toxicity [
There are no current endotoxin exposure limits regulated in the US by Occupation Safety and Health Administration (OSHA) [
The present study is part of the California Dairy Environmental Health Research Initiative (Cal-DEHRI). Previous studies on these workers have reported a significant increase in respiratory symptoms in dairy workers compared with controls [
Workers were recruited from 13 free-stall dairies with over 1000 cows in California’s San Joaquin Valley. Each farm was visited for 2 to 7 consecutive days. The control facility was a vegetable processing plant in Gilroy, CA. The control was chosen because it had similar socio-demographic characteristics as the dairy workers and lacked exposure to animals. Single cross-shift measurements of each worker were collected from June to October 2008. Further details of participant recruitment and health measurements are described in [
Following UC Davis Institutional Review Board approval, subjects were recruited with the following eligibility: age 18+ years, male, able to wear the samplers for their entire work-shift (more than 6 hrs), speak English or Spanish, and able to perform Pulmonary Function Tests (PFTs). Detailed health measurements, demographics, study design, and analysis can be found in [
Pulmonary function was measured using an Easy One Portable Spirometer (NDD Medical Technologies, Andover, MA). The National Institute for Occupational Safety and Health (NIOSH) protocol was followed and technicians were NIOSH certified. Statistical modeling of pulmonary function changes examined a mixed effects model that jointly examines pre- and post-FEV1 and FVC by including a shift factor (before the start of the shift and at the end of the shift). FEV1 is the volume of air forcefully expelled from the point of maximum inhalation in the first second and is an indicator of obstructive conditions reducing exhalation speed. FVC is the maximum volume of air exhaled forcefully from the point of maximum inhalation and indicates restrictive conditions and very severe obstructive diseases.
A single cross-shift measurement was performed on each enrolled worker. Workers wore personal monitors for the duration of their work-shift, including lunch and breaks. Sampling methods and analysis can be found in further detail in [
Filter samples were analyzed for biologically active endotoxin using recombinant Factor C (rFC) assay (Lonza, Inc., Walkersville, MD). Samples were shipped over night on dry ice to Colorado State University for rFC analysis. The method was described in detail in [
Stata 12 software was used for all statistical analyses. Exposure measures (i.e., IPM, PM2.5, endotoxin in IPM fraction and PM2.5 fraction) were log-transformed to correct for positive skew and mean-centered to reduce multicollinearity when examining interactions. Multiple linear regression models were estimated for exposure measures to examine differences between dairy and control workers. Mixed linear regression models were estimated to examine the association between worker exposure to pollutants (explanatory variables) and cross-shift lung function as measured by FEV1 and FVC (response variables). Lung function changes and interactions by pollutant exposures during the shift were examined as time main and interaction effects, where the pre-shift lung function measure was coded as time 1 and the post-shift measure as time 2 (pre-shift minus post-shift lung function measures). Separate analyses were conducted for FEV1 and FVC lung function measures. In each case, the lung function measure at pre- and post-shift was the response variable, and the four exposure measures, time (pre-shift and post-shift) and other covariates (age, race, height, years in the US, country or origin, education level, family income, smoking status, exposure to second-hand smoke, number of days since last day off, PPE use, years worked on a dairy, length of work-shift, hours spent in an enclosed cab, dairy facility, herd size, tasks, RH, and temperature) were entered as explanatory variables (
The male dairy workers averaged 32.9 years (SD = 10.9), mostly (94.2%) Latino immigrants from Mexico, and had spent on average 12 years in the US (
Dairy workers (n = 185) | Control workers (n = 45) | |||||||
---|---|---|---|---|---|---|---|---|
Mean (SD) | Median | n | % | Mean (SD) | Median | n | % | |
Age (years) | 32.9 (10.9) | 31 | 34.8 (11.6) | 32.5 | ||||
Years spent in the US | 12.08 (8.1) | 10 | 8.9 (8.9) | 5 | ||||
Height (cm) | 169.4 (5.9) | 169 | 165.0 (7.2) | 166 | ||||
BMI | 27.0 (4.1) | 27.2 | 27.7 (3.1) | 27.4 | ||||
Age (years) | ||||||||
19 - 25 | 57 | 30.8 | 12 | 26.7 | ||||
26 - 35 | 66 | 35.7 | 14 | 31.1 | ||||
36 - 45 | 37 | 20.0 | 10 | 22.2 | ||||
46 - 55 | 18 | 9.7 | 8 | 17.8 | ||||
56 - 70 | 7 | 3.8 | 1 | 2.2 | ||||
Yearly family income | ||||||||
$0 - 10,000 | 9 | 4.9 | 10 | 22.2 | ||||
$10,001 - 20,000 | 35 | 18.9 | 18 | 40.0 | ||||
$20,001 - 30,000 | 103 | 55.7 | 7 | 15.6 | ||||
$30,001 - 50,000 | 24 | 13.0 | 6 | 13.3 | ||||
$50,001+ | 1 | 0.5 | 1 | 2.2 | ||||
No response | 13 | 7.0 | 3 | 6.7 | ||||
Education | ||||||||
None | 5 | 2.7 | 0 | 0.0 | ||||
Primary (grades 1-6) | 90 | 48.6 | 14 | 31.1 | ||||
Junior high (grades 7-9) | 57 | 30.8 | 21 | 46.7 | ||||
High school (grades 10-12) | 30 | 16.2 | 8 | 17.8 | ||||
Some college (grade > 12) | 3 | 1.6 | 2 | 4.4 | ||||
Ethnicity | ||||||||
Latino | 171 | 92.4 | 40 | 88.9 | ||||
Non-Latino | 9 | 4.9 | 1 | 2.2 | ||||
No response | 5 | 2.7 | 4 | 8.9 | ||||
Race | ||||||||
White | 61 | 32 | ||||||
Indigenous Indian/S American Indian | 109 | 59 | ||||||
Other | 8 | 5 | ||||||
Declined | 7 | 4 | ||||||
Country of origin | ||||||||
United States | 4 | 2.2 | 3 | 6.7 | ||||
Mexico | 171 | 92.4 | 42 | 93.3 | ||||
Other Central/South America | 5 | 2.7 | 0 | 0.0 | ||||
Portugal | 5 | 2.7 | 0 | 0.0 |
Dairy workers (n = 185) | Control workers (n = 45) | |||||||
---|---|---|---|---|---|---|---|---|
Mean (SD) | Median | n | % | Mean (SD) | Median | n | % | |
Never smokers | 101 | 54.6 | 31 | 68.9 | ||||
Former smokers | 36 | 19.5 | 8 | 17.8 | ||||
Current smokers | 48 | 25.9 | 6 | 13.3 | ||||
Pack yearsa | 5.5 (7.1) | 3.1 | 3.72 (4.7) | 1.7 | ||||
Cigarettes per dayb | 8.2 (1) | 5 | 4.5 (1.5) | 2.5 | ||||
Shift use | 25 | 13.5 | 0 | 0.0 | ||||
Cigarettes per shiftc | 4 (3.3) | 3 | 0 | 0 | ||||
Exposure to second-hand smoke | ||||||||
None | 97 | 52.4 | 27 | 60.0 | ||||
At home only | 42 | 22.7 | 13 | 28.9 | ||||
At work only | 43 | 23.2 | 5 | 11.1 | ||||
At home and work | 3 | 1.6 | 0 | 0.0 | ||||
Time exposed at work during observed shift (mins) | 26.9 (7.5) | 10 | 0.2 (0.2) | 0.5 |
aPack-years calculated among ever smokers, n = 79; 74 dairy workers and 15 control workers, 2 missing. bCigarettes per day among ever smokers. cCigarettes per shift among workers who smoked during shift, n = 25 dairy workers.
Dairy workers (n = 185) | Control workers (n = 45) | |||||||
---|---|---|---|---|---|---|---|---|
Mean (SD) | Median | n | % | Mean (SD) | Median | n | % | |
Work history | ||||||||
Years in agriculture | 19.2 (12.6) | 17.0 | 8.3 (6.5) | 6.0 | ||||
Years working on any dairy | 8.7 (8.8) | 5.0 | 0 | 0.0 | ||||
History of PPE usea | ||||||||
More than half the time | 16 | 8.7 | 14 | 31.1 | ||||
Up to half the time | 26 | 14.0 | 13 | 28.9 | ||||
Never or rarely | 142 | 76.8 | 18 | 40.0 | ||||
No response | 1 | 0.5 | 0 | 0.0 | ||||
Observed shift | ||||||||
Length of work-shift (hrs) | 9.1 (0.9) | 9.0 | 8.6 (0.2) | 8.0 | ||||
Time spent working in dusty environment (mins) | 145 (200) | 1.0 | 2.4 (3.8) | 0.0 | ||||
# of days worked since last day | 3.1 (2.1) | 3.0 | 3.9 (1.6) | 4.0 | ||||
Mins spent in an enclosed cabb | 245 (62) | 0 | 0 | 0 | ||||
PPE usea | ||||||||
Yes | 1 | 0.5 | 2 | 4.5 | ||||
No | 26 | 14.1 | 43 | 95.5 | ||||
No response | 158 | 85.4 | 0 | 0.0 |
aIncludes use of mask, N95 respirator, or cartridge respirator. bOnly 15 dairy workers who spent time in enclosed cab included.
Dairy workers had spent more time working in an agricultural setting than the controls with a mean of 19.2 years (SD = 12.6) and 8.3 years (SD = 6.5), respectively. None of the controls had previously worked on a dairy. PPE use was higher (p < 0.001) among the control workers at 60%. Only 22.7% of the dairy workers reported using PPE either up to half of the time or more than half of the time during their shift. During the observed shift none of the dairy workers had reported wearing PPE more than half of the time. On average dairy workers’ shifts were half an hour longer than the control workers, at 9.1 hrs (SD = 0.9) as compared to 8.6 hrs (SD = 0.2), respectively.
Personal exposures to IPM, PM2.5 and endotoxin in both fractions are reported in
Dairy workers | |||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Geomean | 95% CI | % samples < LOD | Min | 25th | 50th | 75th | Max | ||||||
IPM (μg/m3) | 800.0 | 735.7, 870.0 | 0.0 | 191.0 | 564.3 | 757.8 | 1129.1 | 4949.5 | |||||
PM2.5 (μg/m3) | 33.0 | 29.8, 36.4 | 0.0 | 7.1 | 20.5 | 30.4 | 50.2 | 252.7 | |||||
IPM endotoxin (EU/m3) | 331.5 | 294.8, 372.8 | 0.0 | 45.2 | 188.7 | 312.4 | 583.4 | 2061.3 | |||||
PM2.5 endotoxin (EU/m3) | 3.3 | 2.9, 3.8 | 0.0 | 0.3 | 1.7 | 3.1 | 6.9 | 29.5 | |||||
Control workers | |||||||||||||
Geomean | 95% CI | % samples < LOD | Min | 25th | 50th | 75th | Max | ||||||
IPM (μg/m3) | 408.4 | 338.8, 594.7 | 0.0 | 112.5 | 273.9 | 328.1 | 690.5 | 1477.5 | |||||
PM2.5 (μg/m3) | 19.6 | 14.8, 25.9 | 0.0 | 2.1 | 10.5 | 18.9 | 33.8 | 168.4 | |||||
IPM endotoxin (EU/m3) | 12.5 | 6.2, 25.2 | 0.0 | 0.0 | 4.5 | 10.9 | 60.6 | 1279.4 | |||||
PM2.5 endotoxin (EU/m3) | 0.6 | 0.4, 0.9 | 15.5 | 0.0 | 0.2 | 0.4 | 0.8 | 12.1 | |||||
aInhalable particulate matter (IPM). bParticulate matter less than 2.5 μm in diameter (PM2.5).
No significant difference was observed in baseline FEV1 and FVC between dairy workers and control workers (p = 0.180, R2 = 0.524 and p = 0.218, R2 = 0.543, respectively) after controlling for age and height; smoking and second-hand exposure were not significant. The subgroup of dairy workers observed in the current paper experienced a crude-change cross-shift decline in FEV1 and FVC of −44.3 mL and −35.6 mL, respectively, in comparison to controls, who had cross-shift levels in FEV1 and FVC of +18.6 mL and +60.8 mL, respectively. There was a significant difference between dairy and control workers in cross-shift FEV1 and FVC when controlling for age and height (p = 0.029, R2 = 0.021 and p = 0.006, R2 = 0.037, respectively). Cross-shift FEV1 and FVC in dairy workers declined significantly (t = −3.53 (184) p = 0.001, and, t = −2.75 (184), p = 0.006, respectively). In controls, cross-shift FEV1 (t = 0.79 (44), p = 0.436) did not change and FVC increased (t = 2.12 (44), p = 0.04). Findings in the current paper are consistent with results reporting lower pulmonary function in dairy workers than in controls in a larger set of subjects from the same facilities [
A mixed linear regression was performed for FEV1 among dairy and control workers. Statistically significant covariates included: age, race, number of days since last day off, PPE use, height, and temperature (
FEV1, L/sec | ||||||
---|---|---|---|---|---|---|
Coef. | 95% CI | p-value | ||||
Age | −0.029 | −0.034 | −0.024 | <0.001 | ||
Race | ||||||
White | ||||||
Indigenous Indian/S American Indian | 0.081 | −0.042 | 0.199 | 0.199 | ||
Other | −0.430 | −0.713 | 0.003 | 0.003 | ||
Days worked since last day off | −0.024 | −0.050 | 0.002 | 0.075 | ||
LnPM2.5 endotoxin (EU/m3)a | −0.046 | −0.129 | 0.564 | 0.564 | ||
PPE history use | 0.224 | 0.076 | 0.003 | 0.003 | ||
Heighta | −0.016 | −0.054 | 0.023 | 0.424 | ||
Temperaturea | −0.005 | −0.010 | 0.000 | 0.038 | ||
FVC, L/sec | ||||||
Coef. | 95% CI | p-value | ||||
Age | −0.029 | −0.035 | −0.023 | <0.001 | ||
LnPM2.5 endotoxin (EU/m3)a | −0.022 | −0.121 | 0.076 | 0.652 | ||
PPE history use | 0.194 | −0.023 | 0.370 | 0.031 | ||
Height (10 cm)a | 0.065 | 0.052 | 0.078 | <0.001 | ||
Temperaturea | −0.006 | −0.012 | −0.001 | 0.018 | ||
aData centered.
(p < 0.001), decreasing 1 ml instead of 0.2 ml per 10 years. Older control workers also had lower pre- and post-shift FEV1 (p < 0.001), however, for every 10 year increase in age, FEV1 declined by 0.2 ml. With respect to race, dairy workers who identified as being “Other” had lower FEV1 than those who identified as being White (p = 0.023). However, workers who identified as being Indigenous Indian/S American Indian and those who declined did not differ from those who identified as being White (p = 0.596). There was no significant difference in FEV1 among control workers who identified as being Indigenous Indian/S American Indian, those who declined and “Other” (p = 0.824, p = 0.293, and 0.273, respectively). Workers wearing a PPE showed better cross- shift FEV1 by 0.3 ml (p < 0.001) than those who did not. There was no significant change observed in FEV1 among control workers and use of PPE (p = 0.090). Finally, the more days dairy workers had worked in a row, was marginally significant in decrease of cross-shift FEV1 (p = 0.075). The more days workers had worked in a row was not significant in cross-shift FEV1 among control workers (p = 0.309).
Analyses showed significant interactions between PM2.5 endotoxin exposure and dairy worker height and time of FEV1 measure (pre-, post-shift) and temperature of sampling day. There was no significance observed between PM2.5 endotoxin exposure and control worker height and time of FEV1 measure and temperature of sampling day (p = 0.112 and p = 0.409, respectively). The observed interactions for dairy workers indicate that the effect of exposure on FEV1 differed by worker height and that cross-shift changes depend on temperature. To further study these interactions, we examined the conditional relationships for workers at different heights (mean ± 1SD: 163 cm, 169 cm, 175 cm) and for sampling work-shifts with different temperatures (mean ± 1SD: 16˚C, 22˚C, 28˚C). For the endotoxin exposure-by-height interaction, findings show a statistically significant negative association among taller workers (p = 0.006) and no association among workers of average or shorter height (p = 0.268 and p = 0.274, respectively). Further investigations of cross-shift by temperature interaction showed a significant cross-shift decline in FEV1 when temperature was ≥28˚C (p = 0.019 and p = 0.002, respectively). When workers worked during shifts when temperature was relatively low (16˚C) there was no significant cross- shift change in FEV1 (p = 0.820).
A mixed linear regression was also performed for dairy and control workers FVC results (
Similar to our findings for FEV1, an interaction between dairy worker height and exposure to PM2.5 endotoxin was observed. To further investigate this interaction, the conditional relationships between FVC and PM2.5 endotoxin for workers at different heights (mean ± 1SD: 163 cm, 169 cm, 175 cm) were examined. These analyses showed a significant negative association among the taller dairy workers (p = 0.003) between PM2.5 endotoxin exposure and FVC, a significant positive association between shorter workers (p = 0.028), and no association among average height workers (p = 0.102 and p = 0.652). There was no significant association between height and exposure to PM2.5 endotoxin in control workers at shorter, average, and taller heights (p = 0.783, p = 0.510, and p = 0.512, respectively). The interaction between temperature and time was also further investigated to determine temperature effects on cross-shift FVC. These analyses showed a decline in cross-shift FVC (p = 0.021) at higher temperature and no association when temperatures were average or below average among dairy workers (p = 0.078 and p = 0.806, respectively). There was no significant interaction between temperature and time (pre- minus post-shift) with respect to FVC for control workers (p = 0.594).
Personal exposure to endotoxin in PM2.5 among Californian dairy workers has not been previously reported. Here we show that dairy workers had about five times higher personal exposure to PM2.5 endotoxin compared to controls, which is similar to Mitchell et al. [
Job tasks, variation in dairy manure management, meteorological data, wind speed, and RH have been reported to influence personal and area IPM endotoxin concentration on these dairies [
Personal exposures to PM2.5 endotoxin was weakly correlated with PM2.5 concentration (r2 = 0.16, p < 0.05) and inhalable PM endotoxin (r2 = 0.35, p < 0.01), but not with inhalable PM concentration. Endotoxin in IPM in a study by Burch et al. [
In this study, we found that higher endotoxin exposure in the PM2.5 size fraction appeared to be associated with reduced lung function, but only in taller workers. Specifically, we found significant negative associations between endotoxin exposure and FEV1 as well as FVC among taller workers. There was a marginally significant exposure to PM2.5 endotoxin among taller workers (p = 0.075). This novel finding, however, should be replicated with a larger sample size to further investigate the relationship between PM2.5 endotoxin exposure and lung function. Smoking background and primary task was further explored to observe if there was any differences in regards to workers’ height (i.e. taller workers had a greater history of smoking). No significant differences were observed among workers height and smoking background. There was also no significant differences among height and tasks on the dairy, however, maintenance workers were a bit taller with an average height of 174.2 cm, but there were only 5 workers in this group. In this study, higher daily average temperatures were associated with the cross-shift declines in FEV1 and FVC. Donaldson et al. [
The number of days worked since the last day off was marginally significant with respect to cross-shift FEV1. Workers who worked more days in a row had lower cross-shift FEV1. Bonlokke et al. [
Limitations included the need for a larger sample size so that smaller associations between lung function and PM2.5 endotoxin exposure may be detected with better statistical power. In observational studies such as this, confounding is a concern. In this case, control workers had lower smoking prevalence and secondhand smoke exposure than dairy workers. Our analyses, however, showed that neither was a significant covariate in FEV1 and FVC mixed linear regression models. As discussed in [
This study found a negative association between personal exposure to PM2.5 endotoxin exposure and decreases in dairy worker lung function (cross-shift) among taller workers. Higher temperatures during work-shifts were found to be associated with cross-shift decline in FEV1 and FVC, and self-reported use of PPE appeared protective. Replications in other dairies, locations, and other measures, such as gram positive bacteria or molds/fungi, are necessary. Further investigation on how tasks on the dairy influence exposure to PM2.5 endotoxin can help in elucidating the source of PM2.5 endotoxin, and potential health effects. Longitudinal studies in lung function could potential help in better understanding the cumulative effect of endotoxin exposure. In future studies, assessing task-specific exposure is important to mediate efforts to reduce decline in worker lung function and pollutant exposure.
The authors would like to thank Rebecca Gallo for all of her help in preparing and organizing the samples. They would also like to thank Tracey Armitage for her advice on statistics. Funding sources: CA Ag Center, HICAHS NIOSH OH008085.