ES&T OUTLOOK Crop losses from air pollutants Air pollutants are being blamed for crop losses estimated at several billion dollars a year. The National Crop Loss Assessment Network is providing more data It is generally agreed that ozone, sulfur dioxide, and nitrogen dioxide cause about 90% of the crop damage induced by gaseous air pollutants in this country. Before 1980, however, there were only rough estimates of the actual losses, based on very limited and usually quite inadequate experimental data. Even now, assessments of crop loss are not nearly as good as they might be with additional experimental data covering a greater number of crops and more pollutants and their mixtures. A knowledge of crop reductions from air pollution is important for several reasons. It satisfies a natural curiosity—anyone might wonder how yields might change if we reduced these pollutants to natural background levels. Estimates provide us with data that are absolutely necessary for making meaningful cost-benefit analyses; we need to know the benefits provided to agriculture by current pollution controls and the agricultural losses induced by current levels of pollution. Also, the Clean Air Act re quires that the secondary National Ambient Air Quality Standards be based on the public welfare, which is defined as including but is not limited to, effects on soils, water, crops, vege tation, manufactured materials, ani mals, wildlife, weather, visibility, and climate. Without reliable knowledge of the effects of pollutants on crops, the EPA administrator cannot take these effects into account when setting the standards. Before 1976, no research had been completed that provided reliable data relating a range of pollutant exposures to crop yields. The experiments had one or more of the following deficien cies: The usual response measured was 0013-936X/82/0916-0495A$01.25/0
© 1 9 8 2 American Chemical Society
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foliar injury. It has little relationship to yield except for crops such as lettuce and tobacco. The methods that were used to expose the crops to pollutants varied widely. Many experiments did not include adequate measurements of pollutant concentrations. The methods of stating these were not consistent. As a result, the doses in one study often could not be compared to those in another. Because of these research deficiencies and because it was necessary to estimate crop losses resulting from air pollution in order to provide a better scientific basis for the secondary standards, the National Crop Loss Assessment Network ( N C L A N ) was established in 1980. Funding for the program is provided primarily by EPA. At the June 1982 meeting of the Air Pollution Control Association in New Orleans, several N C L A N researchers reported their results in a session chaired by Leonard H. Weinstein of Boyce Thompson Institute in Ithaca, N . Y . The N C L A N program has four components. The first is to carry out experiments that reliably relate doses of pollutants to yields for those crops that are economically important. The second is to integrate these crop losses over entire regions using the doseresponse information gained in the experiments, the acreage devoted to the crop, and the pollutant levels in each county. The third is to assess the amount of money lost each year from the effects of these pollutants on agriculture, and the fourth is to create models that relate crop yields to a variety of factors including the level of pollutant, water stress, stage of crop development, and temperature. The
models would provide a means to more accurately assess losses from air pollution. So far, the first aim of N C L A N has required the greatest amount of funding. The experimental part of the program is performed at six sites around the country, each of which represents a major crop-growing region. The sites are located at the Boyce Thompson Institute, Ithaca, N.Y.; North Carolina State University, Raleigh, N.C.; Beltsville Agricultural Research Center, Beltsville, Md.; Argonne National Laboratory, Argonne, 111.; University of California, Riverside, Calif.; and Lawrence Livermore Laboratory, Livermore, Calif. Extensive areas of the country, such as Texas and the delta region of the deep South, are not represented by the sites. The sites were chosen because each has current or potential pollution problems and because each has a research group with long experience in the study of the effects of air pollutants on crop production. At first, more research stations and many more individual studies were planned. However, funding for N C L A N is less than what it was projected to be according to the original plans and trends in funding. The EPA funding for fiscal year 1982 was $2.7 million. Only $2 million has been requested for fiscal year 1983, but the actual appropriation will probably be less than this. Therefore, both the number of sites and number of experiments will be severely restricted. Experimental design The studies that are under way to obtain a dose-response relationship between air pollution and crop yield use primarily a single standardized
Open-top chambers are used for nearly all the experiments in the National Crop Loss Assessment Network
A. Fiberglass particulate filter B. Sheet metal box c. % HP axial blade fan D. Connecting duct E. Upper panel F. Double-walled lower duct panel with perforated inner walls G. Gas injection port
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Environ. Sci. Technol., V o l . 16, No. 9, 1982
research approach. Crops are grown in open-top chambers constructed with aluminum channel frames covered with clear plastic film (see Figure). The chambers are 3 m in diameter and 2.5 m in height and are equipped with a fan to introduce about three changes of air per minute through a manifold surrounding the lower half of the chamber. If the chamber is used as an experimental control, the air passes through both particulate and charcoal filters that reduce the ozone level to about 0.025 ppm (considered to be natural background). If the chamber is not a control, the air passes through only a particulate filter, whose main function is to keep the chamber walls from becoming dusty. Different doses of pollutant are obtained either by adding gases at various concentrations to the ambient pollutant load or by partial filtration to reduce the ambient pollution. Agricultural practices that are most common for the particular crop and region are used in the experiments. The only exception to this is that water is usually added as needed even for those crops that are not usually irrigated. This is done for an entirely practical reason—to eliminate the possibility that the entire experiment could be lost from drought. Open-top chambers seem to be an almost ideal experimental method. Several studies have shown that chambers have little effect on growth and yield. To further substantiate this conclusion, companion plots outside the chambers were used in most experiments after 1980. N o chamber was placed over the companion plot, and except for irrigation and the addition of pollutant, the crop was treated in the same way as the crop inside the chamber. Pollutant or pollutants are added to the open-top chambers during the hours in the day when the level of that pollutant is normally the highest. In the case of ozone, this is between the hours of 9:00 A . M . and 4:00 P.M. local standard time. Most studies use at least 20 chambers because earlier research suggested that 20 is an optimum for statistically meaningful results within cost constraints. A greater number of chambers are employed in the experiments that measure the effects of more than one pollutant. In many experiments prior to 1976, plants were exposed to very high levels of pollutants only a few times during the growing season. In contrast, the exposure levels in these N C L A N experiments are those encountered or potentially encountered by crops in the region, and the exposure is carried on
During the growing season, ozone levels are high enough to reduce the yields of many cropsE
Average ozone level |
I Not estimated
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.050-.060 ppm
|
I .020-.030 ppm
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.060-.070 ppm
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| .030-.040 ppm
| |
.070-.080 ppm
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| .040-.050 ppm
[ e j Sites in the National Crop Loss Assessment Network
a
Average county-levei ozone concentrations from June to September are estimated according to a procedure developed by J.A Reagan, EPA. The concentrations are the averages of ozone leveis from the 7-h period in the day when concentrations are the highest.
Source: "Effects of Air Pollution on Farm Commodities," Proceedings of the Symposium. February 1982, Izaak Walton League of America.
The National Crop Loss Assessment Network has found dose-response relationships for ozone for a number of important crops. Nearly all of them show a linear relationship. Field corn is a major exception. Typical examples of dose- response curves are shown below.
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80 60 Kidney bean a (California light red)
40 20 0
.04 .08 .12 .16 7-h/day mean O3 concentration
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.04 .08 .12 .16 7-h/day mean O3 concentration
0
.04 .08 .12 .16 7-h/day mean O3 concentration
— A Corn (3780), 1981" • Corn (397), 1981 1
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J_ _L .04 .08 .12 .16 7-h/day mean O3 concentration
Source: Journal of the Air Pollution
Control Association,
April 1982,
b
Source: "Effects of Air Pollution on Farm Commodities," Proceedings of the Symposium, February 1982, Izaak Walton League of America.
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background were significantly reduced from yields at background. Thus, there was almost always a meaningful difference between the productivity with charcoal-filtered air and that with ambient air, showing that the ambient air at the experimental sites was having a substantial effect on the output of crops. For example, the peanut yield was reduced 15% by ambient air at the Raleigh, N.C., site. A comparison of the ozone map of the U.S. (showing ozone levels from July to September) with ozone levels used in the experiments reveals that the lowest two ozone levels above the control in the experiments were not higher than average ozone concentraOzone injury: Potato plant leaves on the far left were grown in charcoal-filtered air.tions occurring in many agricultural areas. Therefore, since these two lowThe leaves on the right were grown in ozone-contaminated air. est levels of ozone caused significant crop reductions for a number of imfor a specified amount of time every to help select cultivars for field testing portant crops, it is readily apparent day during the growing season except and to determine relative cultivar that a large portion of the agricultural when it rains. The ambient levels of sensitivity for use in economic assessland area of the U.S. is experiencing ozone in Riverside, Calif., are so high ments. ZAPS cannot be used to find an that for two of the treatment levels, it absolute percent yield reduction be- oxidant levels capable of decreasing crop yields. is necessary to filter out different cause there is no way to set up a control fractions of the ambient ozone rather with charcoal-filtered air. Another This is also illustrated qualitatively than adding it. problem is that it is impossible to conby another experiment at the Beltsville Probes to monitor the pollutant level trol exposure levels precisely; they Agricultural Research Center. Two are placed in the center of each depend upon the speed and direction of greenhouses are used: one with ambichamber. A number of other variables the wind. ent air, one with charcoal-filtered air. are measured at the sites. Ambient O3 A number of varieties of soybean and and SO2 and the amount of rainfall are Results lima bean are being grown with idenmonitored at all sites. NO2 and CO2 tical treatment in each greenhouse. By For the most part, economically are monitored at some. Also, at a observing the plants, it can be seen that important crops are being studied with number of sites, measurements of solar open-top chambers. The majority of most varieties of these crops are more radiation, soil temperature, soil mois- the crops are among the 10 agriculhealthy in the charcoal-filtered air. In ture, and wind speed and direction are tural commodities that produce the general, the leaves are greener, espetaken. The chemical composition of greatest amount of revenue in the U.S. cially those closest to the soil, which the rainfall is measured at half the (see Table). tend to turn yellow and fall off first stations as part of the National Atwhen a plant is under stress. The air in Most of the open-top chamber mospheric Deposition Program. Beltsville is polluted but not particustudies concerned the effect of ozone larly so compared with many rural The primary measurement taken in alone. Soybeans, cotton, and peanuts all the open-top chamber experi- are the important crops whose yields areas in the East. The usual summer ozone level is about 0.05 ppm, and it ments—and the one upon which most were found to be reduced significantly rarely exceeds the 1 -h standard of 0.12 of the results have been based thus by the ozone levels found in rural ppm. far—is the quantity of yield at harvest. areas. Citrus fruits are also affected, This is usually expressed in terms of but no dose-response relationships A number of experiments in the grams of marketable produce per plant have been obtained yet for these crops. NCLAN program were set up to and sometimes as grams of marketable Field corn, forage plants, wheat, and measure the combined effects of two produce per meter of row. other grains seemed to be less susceppollutants on yields. In most cases, the Besides open-top chambers, the only tible. Their yields are probably not impacts seemed to be additive rather other experimental method that has being decreased to an important extent than synergistic, but in some studies been used to any extent is the Zonal by current ozone levels. However, a the effects appeared synergistic. For Air Pollution System (ZAPS). This is mixture of ozone and SO2 at the levels example, at Argonne National Laboexactly what the acronym implies. A found in many areas where alfalfa is ratory, the soybean cultivar Northup long perforated pipe is suspended just grown may be affecting it. Dose-reKing 1492 was exposed to SO2 and above the crop in the open field. The sponse studies for mixtures of polluNO2 in the presence of ambient ozone. pipe is used to give the plants acute tants on alfalfa are needed. Combinations of the pollutants deexposures of ozone, SO2, or NO2 for creased yields by 9-18% at concenResults from the open-top chamber three hours usually twice weekly experiments could be discussed in trations causing no decreases when throughout the growing season. Ex- great detail. Most of them, however, they occurred alone. On the other posures are made only when a steady can be described very simply. Except hand, these two pollutants seemed to wind (>3 mph) intersects the pipe at for field corn and one or two minor have no interactive effects on the soyan angle of 45° or more. So far ZAPS crops, a linear relationship was found bean cultivar Hodgson exposed at has been used primarily for SO2 between ozone levels and crop yields. Boyce Thompson Institute. At the studies. Beltsville, Md., site, no interactions Even more surprisingly, nearly all the In general, this system is employed yields obtained at levels of ozone above were found between O3 and SO2 for 498A
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two soybean cultivars and for tomatoes, but for snap beans the effects of these two pollutants appeared synergistic. Results from many of the experiments seem quite definitive, but more work needs to be done, especially on the effects of SO2 and on the combined effects of more than one pollutant. Howard E. Heggestad, senior scientist at Beltsville Agricultural Research Center, said that mixtures of all three pollutants—ozone, N 0 2 , and SO2— should be studied at the low concentrations that might be enountered in rural areas. He suggested that there are some reasons to believe that positive benefits might be found at certain low levels. Economic assessments Basically two types of economic assessment have been performed to determine the economic loss from ozone alone. One type of analysis was prepared by Walter W. Heck et al. for the Izaak Walton League Symposium, "Effects of Air Pollution on Farm Commodities." This assessment took dose-response relationships obtained from open-top chamber studies and integrated the crop reductions for four economically important crops over entire regions using 1978 ozone levels and 1978 crop yield information. In this way, the total amounts of the four crops lost to ozone in the regions were calculated. Economic losses for the entire country were then found by adding together the losses for each region and multiplying these sums by
Acres harvested and cash value of major U.S. crops in 1978 Crop
Millions of acres harvested
Value in $ (billions)
Corn for grain
70
15.9
Soybeans
63
12.5
Hay
62
6.6
Wheat
57
5.3
Cotton
12
3.0
