MOVEMENT OF CHEMICALS IN SOILS

I. INTRODUCTION

Agriculture is the foundation of the region's economy.

Major increases in agricultural production have occurred because of the extensive use of agricultural chemicals.

A. USE OF AGRICULTURE CHEMICALS

In the corn belt states, in 1988, 98% of the corn acreage received herbicide treatment and 34% received insecticide treatment. Nitrogen, herbicides, and insecticides used on corn in this region averaged 150, 3 and 1 lb/acre.

B. CONCERN

The intensive use of agricultural chemicals has raised a growing public concern about the impact on groundwater quality, since over 90% of rural residents in the U.S. depend on ground water as a source of drinking water.

More and more frequently we see reports of nitrate-nitrogen and pesticides in the drinking water.

Groundwater supplies drinking water to approximately 53% of the nation's population and to 97% of the population living in rural areas. Groundwater also provides about 55% of the water used by livestock. Lant - 1993

FACTORS WHICH AFFECT MOVEMENT

A. CHARACTERISTICS OF THE COMPOUND

"Oxidation and reduction (redox) reactions at mineral surfaces are important because many soils undergo reducing conditions at various times during the year, sometimes in a cyclic fashion depending on the season, as a consequence of biological activity, alternate wetting and drying events and reaction with redox-sensitive chemicals in the soil environment. The result is that iron on the surface and in the crystal structure of soil clay minerals is reduced from Fe(III) to Fe(II), causing profound differences in the surface chemistry of the mineral. This in turn, could have a great effect on the nature of the association of organic compounds with the surface. Some herbicides are corrosive, indicating that they can oxidize certain forms of Fe. If Fe in soil minerals is reduced initially, it may be oxidized upon contact with the herbicide and the herbicide will be reduced. This will alter the properties and behavior of the herbicide and the mineral. In addition to the chemical changes that redox reactions produce in the mineral fraction, Fe reduction decreases swelling and hydraulic conductivity and thereby would further influence fate and transport of organics through the soils solution" (Stucki 1993).

The rate of disappearance of alachlor from solution increases overall when the Fe in the clay is reduced from Fe (III) to Fe (II), and is attributed to two processes, namely, an increased level of adsorption to the clay and chemical alteration. Results strongly suggest that the oxidation state of Fe in soil clay minerals is an important factor in determining the fate and properties of agricultural chemicals. Stucki, 1995, p. 106.

The nature and the ability of the product and degradation byproducts to move through the soil. Roy - 1993.

B. SURFACE AND SUBSURFACE HYDROLOGICAL CYCLES

C. PROPERTIES OF THE UNDERLYING SOIL

Texture and organic matter content. Primarily the montmorillonite fraction. more clay = less filtration to groundwater

D. pH

E. MACROPORES Airspace (Sand has a lot-clay has a little)

F. GEOLOGICAL MATERIAL

The wells sampled in Christian County (between Springfield and Decatur) were more likely to be contaminated than those in Edgar County (eastern border, near Terra Haute). One possible explanation may be the age of the tills found in each of the two counties. The till is Edgar County are of the Wisconsinan age and are geologically younger than the tills found in Christian County, which are of the Illinoisan age. The younger, less weathered tills in Edgar County are presumably more chemically active than the soil materials in Christian County. This may result in greater adsorption of the pesticides by the soil particles, thereby reducing the movement of contaminants in groundwater.

G. CROP GROWN

Soil hydraulic properties are significantly different between corn and soybean crops under identical conventional tillage systems. Large differences in infiltration rates measured under corn (more canopy & better infiltration) and soybeans (less canopy & poorer infiltration) were observed. Probably a consequence of crop canopy interactions with timing of rainfall. Rainfall impact can cause surface compaction, which partially seals the soil surface. In addition, small detached particles fill surface pores during sedimentation, further sealing the surface, especially on soils with high silt contents. Work suggests that placement of chemical with respect to the row position also significantly impacts leaching potential. Kamau - 1993.

TIMING AND AMOUNT OF RAINFALL AFTER APPLICATIONS OF CHEMICALS

III. STATUS - NITRATE NITROGEN & PESTICIDES

A million tons of nitrogen as commercial fertilizer is applied to Illinois fields each year. Klubek - 1993.

The US EPA Maximum Contaminant Level (MCL) for NO₃ is 45 mg/L as NO₃. Karny - 1993.

The US EPA standard for NO₃ in drinking water is 10 mg/L as NO₃. Kovacic - 1993.

The US EPA Maximum Contaminant Level (MCL) for Atrazine in drinking water for Atrazine is 3 µg/L. Roy - 1993.

A. SURFACE WATER

In most of Illinois, surface water resources are more likely than groundwater resources to be affected by agricultural chemicals. Taylor (1994) reports that of 150 groundwater supplies tested in Illinois, 24% contained detectable pesticides; however, Atrazine was found in 84% of the surface water supplies tested (with 114 out of 135 water supplies, with nearly 1/4 of the supplies having concentrations equal to or exceeding the safe drinking-water limit set by the EPA for Atrazine Biradar 1995). During a three-year sampling period, the IEPA detected Atrazine at each of 30 stream sites sampled and in 77% of 580 samples collected from streams (Taylor 1989). Risatti 1995.

B. GROUND WATER

It appears that the expected increase in nitrate detections does occur in spring (June); however, this does not appear to be true for pesticides. Pesticides were detected in 14 of 50 wells in January; yet in June, pesticides were found in only 7 wells. In the study, 44% of the wells sampled in Sangamon County had well-water nitrate concentrations which exceeded the US EPA MCL, whereas in Edgar and Christian Counties, this number was only about 25% . Pesticides were detected in a smaller percentage of wells in Sangamon County than what was observed in Edgar and Christian Counties during winter 1991. Atrazine was the pesticide most frequently detected. Karney - 1993.

Half life of Atrazine in the 10-30 cm layer is 2.2 weeks, suggesting that microorganisms possess the capability of anaerobically degrading Atrazine. Roy 1993.

Under anaerobic conditions many facultative bacteria use nitrate as an electron donor, producing nitrogen as a major end product. Observed rates of biodegradation and biotransformation of Atrazine vary widely, ranging from a week to years for anaerobic organisms and from hours to months for aerobic and micro-aerophilic cultures. Risatti - 1995.

The greatest concentrations of Atrazine and degradetes leaving the cropland were transported by tile water. Roy -1993

IV. CONCERNS

A. PESTICIDES

The concern of pesticide contamination of ground water is whether the pesticide contains mutagenic properties. Biradar and Rayburn (1995) performed flow cytometric analysis on Atrazine, simazine, and bentazon for their potential to cause whole-cell clastogenesis in Chinese Hamster Ovary (CHO) cells, and the results suggested the potential of Atrazine to cause whole-cell clastogenicity. The main objective of this study was to examine whether the herbicide levels deemed to be safe by the EPA have the potential to cause any damage to CHO cell chromosomes in culture. The results obtained that the capability of Atrazine (but not simazine and bentazon) to cause chromosome breakages in CHO cells. The breakages were evident at Atrazine concentrations that are deemed to be safe in drinking-water supplies. Biradar - 1995.

B. FERTILIZERS

1. Methemoglobinemia or "blue baby" syndrome

The maximum allowable nitrate concentration in public drinking water is 10 mg/L as nitrogen. The standard was established because high nitrate levels pose a serious risk to infants and can lead to methemoglobinemia, a condition also known as "blue baby" syndrome. In infants, high nitrates can severely limit the transport of oxygen in the bloodstream, which can lead to asphyxia and possible death. Nitrate testing is recommended during the early months of pregnancy and during the first six months of infancy. Karny - 1995.

2. Potential for miscarriages

3. Nitrosamines

Another concern is the reduction on the body of nitrate-N to nitrite-N, which then reacts with amines to form nitrosamines, some of the most potent carcinogens known. Burnham,, 1995, p .132 .

V. COMBATING THE PROBLEM

A. MANAGEMENT PRACTICES

Management practices - 50 ways farmers can protect their groundwater. Beaumont - 1993

Nitrogen

1. set realistic yield goals

2. test the soil

3. credit other nitrogen sources

4. apply nitrogen in the spring

5. use nitrification inhibitors when effective

Scouting

6. scout fields

Insecticides

7. know the economic thresholds for insects

8. consider insect-resistant crop varieties

9. spot-treat insect infestations when possible

10. know how tillage affects insects

11. know how crop rotation affects insects

12. adjust planting and harvesting dates to control insects

13. conserve beneficial insects

14. consider using biological insecticides

Herbicides

15. know the economic thresholds for weeds

16. fine-tune your weed-control program to reduce rates

17. manage crops to compete aggressively with weeds

18. don't increase herbicide rates with conservation tillage

19. band herbicides and cultivate

20. control weeds with cover crops

Pesticide selection

21. determine the organic matter content of your soil

22. determine you soil's potential for leaching

23. determine your pesticide's potential for leaching

24. determine the soil-pesticide interaction ratings

consider other critical pesticide qualities

Water testing and treatment

41. test your water routinely

42. test your water for coliform bacteria and nitrate

43. test your water for pesticides

44. know the signs of contaminants in drinking water

45. select effective water-treatment methods

Miscellaneous

46. store livestock waste wisely

47. have old, underground fuel storage tanks removed

48. dispose of other hazardous waste safely

49. take precautions when irrigating

50. take precautions when chemigating

B. VEGETATIVE FILTER STRIPS

Vegetative filter strips to remove sediment, nutrients and pesticides from runoff. Mitchell - 1993

C. WETLANDS

To use wetlands to remove nutrients and pesticides from combined surface and subsurface flow. Mitchell -1993

Preliminary data (November 1994 - March 1995) indicated that the grassed detention buffer reduced nitrate and orthophosphate loading from the tile drainage to the stream by 67 and 52%, respectively. Kovacic, 1995, p.96.

To enhance biodegradation of Atrazine in fill by increasing the concentration of nutrients and oxygen, and/or by introducing substrates into the fill that stimulated indigenous microbial populations to degrade Atrazine. Roy, 1995, p 117.

D. TILLAGE SYSTEMS

Approximately 25 to 30% of Illinois farmland has been identified as "highly erodible land" (HEL). The Food and Security Act of 1985 mandates that conservation tillage practices be instituted by 1995 for farmers to be "in compliance".

The most effective practice to achieve this status is conservation tillage (a minimum of 30% of the soil covered with crop residue at the time of planting). It is estimated that over 50% of the cropland is tilled under a "reduced till" system. This is achieved by using a tool to till the soil other than a plow. The plow completely rotates the soil so little or none residue is left on the surface of the soil.

The tools or systems which are used to achieve over 30% cover include "no-till" or "reduced till" systems which utilize chisels, sweeps and tandem-discs. Klubek - 1992

In 1991, approximately ½ of the corn and soybean acres in Illinois contains 30% or more of residue on the surface prior to planting. Hornbaker - 1993

Class notes of Dr. Don Stucky.

Revised 6/14/97