Page 705 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

670 SECTION | IX Gases, Solvents and Other Industrial Toxicants

VetBooks.ir chronic pneumonia, chronic intestinal disease, mycotoxi- WISSA, 2006). Static monitors were used to determine
predominantly monthly averages of selected emissions
cosis and others. Temporal connection to petroleum
from oil and gas field operations, including sour gas
sources such as crude oil and previous acute cases is
important in the differentiation. The possible role of plants, gas gathering plants, and batteries (Burstyn et al.,
adverse effects of petroleum compounds on the immune 2007). Assessing exposure parameters for pollutants that
system increasing susceptibility to infectious disease fur- are complex chemical mixtures over a wide area is diffi-
ther complicates the situation. Decreased reproductive cult. A substantial portion of the variability in analytical
performance may have multiple causes. The time delay values occurred in sampling and analytical techniques.
often present between exposure and clinical signs makes Distance from the wells rapidly decreases the concentra-
diagnosis very difficult, if not impossible. Abortions that tions of H 2 S, and the number of sour gas wells increases
result during an acute toxic episode are the easiest to the expected concentration of H 2 S. Including flaring and
associate with the exposure incident. The potential hor- sourness (sulfur content) of the wells improved the model
monal disruption from chemicals that disturb the endo- fit. The primary predictor of SO 2 was the distance of the
crine hormone system relating to conception and sampler to gas processing plants. The results suggest that
pregnancy may not be possible to determine days or SO 2 levels peaked during December to March. There was
weeks after the exposure. poor correlation between the logarithms of H 2 S and SO 2 ,
suggesting that SO 2 levels are not a good predictor for
H 2 S levels. Sampling equipment was operating close to
EPIDEMIOLOGICAL STUDIES: CATTLE
the lower range of sensitivity.
Scott and colleagues used licensed SO 2 emissions from The positive associations with exposure to oil and gas
sour gas plants to estimate the exposure of cattle to air field pollutants that have been reported are given (Waldner,
emissions from oil and gas fields (Scott et al., 2003a d). 2008a d; Waldner and Clark, 2009; Waldner and Stryhn,
Using Alberta Agriculture extension survey data for beef 2008; Waldner et al., 2010). Calving interval in mature
3
cattle, these authors found that there was no association cows exposed to greater than 0.236 μgbenzene/m was
for annual risk of culling, calf crop delivered, stillbirth, estimated to increase by 3 days compared to that of mature
3
twinning, mortality, and calf crop weaned and estimated cows exposed to less than 0.236 μgbenzene/m . Exposure
exposures to SO 2 . For dairy herds using Dairy Herd to SO 2 at the time of calving also increased the risk of calf
Improvement data, there was no association with time to mortality. Exposure to SO 2 ,H 2 S, and volatile organic com-
culling and no association for annual culling risks and pounds measured as benzene or toluene was associated
mortality. There was a small risk for increased calving with a minor increased likelihood of calf treatment after the
interval with high estimated exposure levels. Geographic first month of life. There was a linear relationship between
area was interactive, suggesting the effect of emissions is H 2 S exposure and the risk of treatment. The proximity to
subject to modification by soil type, vegetation, and cli- sour gas flares was not examined. In calves that died,
mate. A study was done in the high density petroleum increasing postnatal exposures to benzene and toluene were
production and cow-calf area of Alberta (Waldner et al., associated with increased odds of respiratory lesions in
2001a,b). Seven beef herds were nonrandomly selected calves older than 3 weeks. Increasing prenatal exposure to
for study, and herds with health problems previously iden- SO 2 increased the odds of lesions in skeletal muscle or
tified with oil and gas field pollution were not included in myocardium. The odds were higher in calves exposed to
the study. Associations were identified for exposure to levels greater than 9 ppb SO 2 . Thyroid lesions of several
unaudited industry reported oil and gas field pollution and types, including hypoplasia and lack of colloid, necrosis
increased calving interval, increased calf mortality, and degeneration, and hyperplasia, were recorded in calves
decreased cow productivity, and increased risk of still- aborted, stillborn and calves dying postnatally. Changes
birth. Lead dioxide-impregnated gauze in Petri plates and were most common in stillborn calves and least in calves
filter paper impregnated with zinc acetate were used as born alive. Calves with thyroid lesions often had other
static monitors to measure SO 2 and H 2 S, respectively. pathology as well.
These static monitors were assayed every 30 days for sul- Immune parameters in yearling cattle from 22 herds
fate and sulfide. Total sulfation increased the risk of odds were examined for effects of ambient PM 1.0 and selected
of nonpregnancy and increased the risk of twinning. PAHs. Immune parameters were peripherally circulating
Increased H 2 S increased the calving-to-calving interval B lymphocytes and CD4, CD8, γδ, and WC1
and increased the risk of nonpregnancy and abortion. The T-lymphocyte subtypes (Bechtel et al., 2009a). The anti-
relationship between nonaudited industrial reported emis- body response to rabies vaccine was also evaluated. No
sions and total sulfation was not reported. associations between PM 1.0 and selected PAHs were dem-
A large epidemiologic study was done on the effects onstrated in the epidemiologic models employed. In
of oil and gas pollution in beef cattle (Waldner, 2008a d; another model, in which exposures to SO 2 ,H 2 S, benzene,