Our study found that the incidence of drift-related pesticide poisoning was higher among female and younger agricultural workers and in western states. These groups were previously found to have a higher incidence of pesticide poisoning . It is not known why the incidence is higher among female and younger agricultural workers, but hypotheses include that these groups are at greater risk of exposure, that they are more susceptible to pesticide toxicity, or that they are more likely to report exposure and illness or seek medical attention. However, we did not observe consistent patterns among workers in other occupations. This finding requires further research to identify the explanation. The higher incidence in the western states may suggest that workers in this region are at higher risk of drift exposure; however, it may also have resulted from better case identification in California and Washington states through their higher staffed surveillance programs, extensive use of workers’ compensation reports in these states, and use of active surveillance for some large drift events in California. Nonoccupational exposure. This study found that more than half of drift-related pesticide poisoning cases resulted from nonoccupational exposures and that 61% of these nonoccupational cases were exposed to fumigants. California data suggest that residents in agriculture-intensive regions have a 69 times higher risk of pesticide poisoning from drift exposure compared with other regions. This may reflect California’s use of active surveillance for some large drift events. Children had the greatest risk among nonoccupational cases. The reasons for this are not known but may be because children have higher pesticide exposures,macetas por mayor greater susceptibility to pesticide toxicity, or because concerned parents are more likely to seek medical attention. Recently several organizations submitted a petition to the U.S. EPA asking the agency to evaluate children’s exposure to pesticide drift and adopt interim prohibitions on the use of drift-prone pesticides near homes, schools, and parks . Contributing factors. Soil fumigation was a major cause of large drift events, accounting for the largest proportion of cases.
Because of the high volatility of fumigants, specific measures are required to prevent emissions after completion of the application. Given the unique drift risks posed by fumigants, U.S. EPA regulates the drift of fumigants separately from non-fumigant pesticides. The U.S. EPA recently adopted new safety requirements for soil fumigants, which took effect in early 2011 and include comprehensive measures designed to reduce the potential for direct fumigant exposures; reduce fumigant emissions; improve planning, training, and communications; and promote early detection and appropriate responses to possible future incidents . Requirements for buffer zones are also strengthened. For example, fumigants that generally require a > 300 foot buffer zone are prohibited within 0.25 miles of “difficult to-evacuate” sites . We found that, of the 738 fumigant-related cases with information on distance, 606 occurred > 0.25 miles from the application site, which suggests that the new buffer zone requirements, independent of other measures to increase safety, may not be sufficient to prevent drift exposure. This study also shows the need to reinforce compliance with weather-related requirements and drift monitoring activities. Moreover, applicators should be alert and careful, especially when close to non-target areas such as adjacent fields, houses, and roads. Applicator carelessness contributed to 79 events , of which 56 events involved aerial applicators. Aerial application was the most frequent application method found in drift events, accounting for 249 events . Drift hazards from aerial applications have been well documented . Applicators should use all available drift management measures and equipment to reduce drift exposure, including new validated drift reduction technologies as they become available. Limitations. This study requires cautious interpretation especially for variables with missing data on many cases . This study also has several limitations. First, our findings likely underestimate the actual magnitude of drift events and cases because case identification principally relies on passive surveillance systems. Such under reporting might have allowed the totals to be appreciably influenced by a handful of California episodes in which active case finding located relatively large numbers of affected people. Pesticide-related illnesses are under reported because of individuals not seeking medical attention , misdiagnosis, and health care provider failure to report cases to public health authorities . Data from the National Agricultural Workers Survey suggests that the pesticide poisoning rates for agricultural workers may be an order of magnitude higher than those identified by the SENSOR-Pesticides and PISP programs . Second, the incidence of drift cases from agricultural applications may have been underestimated by using crude denominators of total population and employment estimates, which may also include those who are not at risk. On the other hand, the incidence for agricultural workers may have been overestimated if the denominator data under counted undocumented workers. Third, the data may include false-positive cases because clinical findings of pesticide poisoning are nonspecific and diagnostic tests are not available or rarely performed. Fourth, when we combined data from SENSOR-Pesticides and PISP, some duplication of cases and mis-classification of variables may have occurred, although we took steps to identify and resolve discrepancies.
Also, SENSOR-Pesticides and PISP may differ in case detection sensitivity because the two programs use slightly different case definitions. Lastly, contributing factor information was not available for 48% of cases, either because an in-depth investigation did not occur or insufficient details were entered into the database. We often based the retrospective coding of contributing factors on limited data, which may have produced some misclassification.Burning fields to remove crop stubble, weeds and pests occurs worldwide, and California’s estimated emissions from the burning of crop residue ranks fifth nationally . These emissions potentially contribute to particulate matter levels in the San Joaquin Valley, which often exceed standards for ambient air each season of the year . Studies have documented thousands of chemicals in smoke; they can exist in gas, liquid and solid form. During burning, plant matter breaks apart and gases condense on particles or form particles. Most particulate matter in smoke is smaller than 2.5 micrometers in diameter and can be transported over long distances . The California Air Resources Board estimates annual tons of particulate matter and gases emitted from field, orchard and weed burning for California counties ; their estimates are derived from burns of crop residue in a laboratory . Studies have documented emissions of 14 semivolatile polycyclic aromatic hydrocarbons , the most abundant of which is naphthalene . A respiratory carcinogen , naphthalene is predominantly found in the gas phase of air sampling, with the remainder measured in the particulate phase . Few ambient air monitoring studies have been conducted in the United States during agricultural burns, either adjacent to burns or in towns and communities . Educational efforts for the general public have mostly focused on smoke from wildfires and have included public health recommendations for those exposed to elevated particulate matter and visibility guidelines for those air levels . CARB has also distributed a lengthy educational pamphlet for farmers . However, it was unknown whether health educational outreach efforts specifically targeting agricultural burning were needed. Particulate matter emissions from field burning in Imperial County — a rural desert county in California’s southeast corner — rank among the highest for any county in the state . The agricultural area of Imperial County is anirrigated desert valley, where a variety of crops including vegetables, hay and grain are grown . Fields of bermudagrass, which is grown both for hay and seed, are burned primarily in the winter, while wheat stubble is burned during the summer. Less than 3% of homes in Imperial County use wood as a house heating fuel . During the winter when night temperatures drop, inversions commonly occur; cooler ground level air, including pollutants, are trapped near the Earth’s surface by an upper layer of warmer air. For fields to be burned,macetas por mayor plastico the Air Pollution Control District requires that the estimated inversion layer must be at 3,000 feet or higher, and the burn must be initiated between 10 a.m. and 3 p.m. Farmers who have applied for burn permits are usually notified by the district the day before the targeted burn date that their fields may be burned. Thus, our air monitoring studies required methods that could be rapidly deployed. Our methods and results are described in greater detail in a report to the funding agency .We selected three schools and one church based on their proximity to burns in previous years and installed portable Environmental Beta Attenuation Monitors . We measured hourly average concentrations of PM2.5 and meteorological variables for 69 days starting on Jan. 14, 2009. E-BAM PM2.5 measurements are not recognized as a Federal Equivalent Method or a Federal Reference Method , one of which is required to determine if levels legally exceed air standards. However, E-BAM measurements have proven comparable to FRM measurements in field tests .
During the E-BAM monitoring period, 15,686 acres were burned on 35 allowable burn days; the acreage burned daily ranged from 0 to 1,400 acres. Average 24-hour PM2.5 concentrations were highest — 12 micrograms per cubic meter — at the northern station and lowest at the western station . The lower levels in Seeley may have been because the predominant wind direction was from the west, and sources of pollution, including burned fields, were predominantly to the east of the Seeley station. All daily PM2.5 levels were below the federal standard for unhealthy air, 35 µg per cubic meter. However, at the Calipatria station the 95th percentile of 24-hour concentrations was above 16 µg per cubic meter, which corresponds to moderate air quality where “aggravation of heart or lung disease in people with cardiopulmonary disease and older adults” is possible . We also compared 8-hour average PM2.5 concentrations at the four locations. There was little difference during the day , with levels slightly lower on field-burn days compared to no field-burn days . In contrast, from the early evening to the morning of the next day , average PM2.5 concentrations on field-burn days were 23% higher than on no-field-burn days. Additionally, on days when there was an agricultural burn within 2 miles of the Calipatria station , during the evening-to-morning period the average 8-hour concentrations were 19.5 to 20.7 µg per cubic meter, 170% higher than on days when there were no burns within 2 miles . Following the burns near the Calipatria station, on the subsequent 2 days when there were no additional burns , the evening-to-morning levels remained slightly above levels on days with no burns . Higher particulate matter levels from evening-to-morning hours associated with agricultural burning in Imperial County are consistent with air pollution dynamics. Air pollutants may rise during the day as the Earth’s surfaces are heated and then be brought down to ground level by the descent of an evening inversion layer. The night and next-day accumulation of smoke is described in a CARB pamphlet for farmers .We monitored five specific burns of 65 to 150 acres of bermudagrass stubble during the E-BAM monitoring period. For four burns, ground-level winds were low at 2 to 3 miles per hour , and the plume from the burn rose up to the apparent height of the inversion layer where it was observed to spread out, sometimes in the opposite direction of the ground wind direction. The ground-level plumes dispersed within about an hour, but the upper plumes remained visible, apparently limited by the inversion layer, until sunset. At one of the five burns, the Dunham burn, the wind speed was higher , and the ground-level smoke plume engulfed a house on the same property as the burned field and drifted onto an adjacent field. We deployed portable particulate matter monitors — active-flow and passive personal DataRAM nephelometers — which continuously measured PM2.5 and PM10 , respectively. This monitoring was done at three locations surrounding each of the five burns for 24 to 72 hours. Two locations were near the burns and were places of public access, homes or telephone poles; the other was at the nearest E-BAM, which was farther away . At the 15 locations, field difficulties including power outages, supply delivery problems and apparent equipment or software malfunctions limited monitoring to 11 and 13 locations for the PM2.5 and PM10 nephelometers, respectively.