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Guidance for Determining the Acceptability of Environmental Fate Studies Conducted with Foreign Soils
On this page
- Purpose
- Background
- Implication of Soil Classification for Foreign Soils
- The United States Soil Classification System
- The Food and Agriculture Organization (FAO) Classification System
- Interim Guidance for the Use of Environmental Fate Data Obtained from Foreign Soils
- Example of the Use of Limited Soil Taxonomy Data in Submitted Studies
- Figures
- References
Purpose
The purpose of this guidance document is to provide a uniform procedure for evaluating the acceptability of foreign soils used in environmental fate studies submitted to the Environmental Protection Agency (EPA) for the registration/reregistration of pesticides in the United States (U.S.). In the ideal case, the registrant verifies that the test soil is representative of the intended use areas within the U.S. In most cases, though, this task is conducted by an EPA reviewer and is based on limited soil taxonomy or other soil data from registrant submitted studies. When sufficient data are available, the reviewer can verify the test soil by using the information in this guidance. It remains the registrant's responsibility, though, to provide the necessary information for verification.
Background
Under the Agency's pesticide data requirements, which are specified in 40 CFR Part 158, selected environmental fate studies are conducted in soils (i.e., leaching, adsorption/desorption, soil metabolism) to determine the persistence and mobility of a pesticide in the environment. The Office of Pesticide Programs' (OPP) current fate and transport guidelines (Subdivision N) state that test soils used in these studies should be collected from typical, intended pesticide use areas in the U.S. Soils from foreign sources may be used in conducting these fate studies if the foreign soil has the same characteristics as soil in the U.S. similar to the proposed use area. Furthermore, complete information on the soil class, textural characterization, pH, and organic matter content should be provided by the registrant so that the reviewer can verify that the chosen soil is representative of U.S. agricultural soils.
EPA's policy concerning the acceptability of studies conducted on foreign soil includes the following elements:
data from studies conducted at field test sites or with test materials that are not characteristic of the U.S. will not be considered in the Agency's risk assessment;
to demonstrate comparability, data should be submitted that shows the lack of substantial or relevant differences between the selected material or test site and the U.S. material or test site; and
once comparability has been established, the Agency will assess the acceptability of the data as described in 40 CFR Part 158.
As mentioned earlier, if a foreign soil is used, data on soil classification as well as physical and chemical properties of soils are needed to indicate its similarity to U.S. agricultural soils from typical use areas. However, the Agency rarely receives information, particularly related to soil classification, when foreign soils are used to conduct Subdivision N guideline studies. For example, many environmental fate studies have been performed with German loamy sand (Speyer 2.2 standard soil) and submitted to the Agency for evaluation without a description of the soil classification or its relevance to U.S. soils. Since this soil has been used as a benchmark soil in many other agricultural and environmental research projects, the Agency was able to obtain the description of this soil and its classification from the open literature such as Riepert and Felgentreu, 2002 and German Standard Soils 
. The German standard soil is a natural soil from Land-und Forstwirtschaftliche Untersuchungsanstalt (Agriculture and Forestry Research Institute) in Speyer, Germany. This soil is classified as a Cambisol, a Soil Unit of the FAO (Food and Agriculture Organization) Soil Classification system, which is equivalent to an Inceptisol under the U.S. Soil Taxonomy classification system and is representative of some agricultural soils of the U.S. Therefore, submitted environmental fate data (such as adsorption/desorption data) using the Speyer 2.2 soil have been considered, in many cases, to be acceptable by the Agency and have been used in the risk assessment process.
Implication of Soil Classification for Foreign Soils
Soil classification systems have been developed to provide scientists and resource managers with generalized information about the nature of a soil found in a particular location. Soil classification also provides information related to the nature of the parent material and the natural distribution of the soil based on soil properties, patterns, and their relationship to the underlying parent materials. In general, environments that share comparable soil forming factors produce similar types of soils globally. This phenomenon makes classification possible. Thus, information related to soil classification of foreign soils is critical in evaluating selected environmental fate studies and their spatial relevance to soils in the U.S. where the pesticide is proposed to be used. With soil classification and other pertinent information, the Agency will be able to evaluate whether the environmental fate studies conducted on foreign soils are appropriate for use in the U.S. pesticide registration process (based on the intended use). Many classification systems are in use worldwide. Descriptions of the most commonly applied U.S. Soil Taxonomy and FAO soil classification systems are discussed below:
The United States Soil Classification System
In 1975, Soil Taxonomy was published by the United States Department of Agriculture's Soil Survey Staff (Soil Survey Staff, 1999). This system for classifying soils has undergone numerous changes since that time, and the ninth edition was published in 2003 (Keys to Soil Taxonomy). U.S. Soil Taxonomy remains one of the most widely used soil classification systems in the world. The current version of the system has six levels of classification in its hierarchical structure. The major divisions in this classification system, which are based on general characteristics and are refined to specific characteristics, are as follows:
- orders
- suborders
- great groups
- subgroups
- families
- series
At the highest level, U.S. Soil Taxonomy places soils in one of 12 categories known as orders:
- Oxisols
- Aridsols
- Mollisols
- Alfisols
- Ultisols
- Spodsols
- Entisols
- Inceptisols
- Vertisols
- Histosols
- Andisols
- Gelisols
(Distribution Maps of Dominant Soil Orders). At its lowest level of organization, the U.S. system of soil classification recognizes approximately 19,000 different soil series. The distributions and brief descriptions of the major soils within the U.S. are shown in Figures 1-13.
The Food and Agriculture Organization (FAO) Classification System
The FAO developed a supra-national classification (World Soil Classification), which conveys useful generalizations about the genesis of soils in relation to the interactive effects of the main soil-forming factors (e.g., parent material, climate). It was first published in the form of the UNESCO Soil Map of the World in 1974 (FAO-UNESCO 1978, 1987). Like the U.S. Soil Taxonomy, it makes class separations on the basis of diagnostic horizons. Some of the descriptive terminology, in simplified form, has been adopted from Soil Taxonomy. Soil Units have been grouped on the basis of generally accepted principles of soil formation to form 26 World Classes. The FAO Soil Units classification is far from ideal (very simple classification system, units are very broad), but it is the only truly international system, incorporating Soil Units used all over the world. Most soils can be accommodated in the system on the basis of their field descriptions.
Interim Guidance for the Use of Environmental Fate Data Obtained from Foreign Soils
The information provided in the studies and in this guidance, along with any other available and relevant information, can be used to decide if foreign soils:
represent U.S soils relevant to proposed pesticide use areas (resulting in the use of the data if the study is otherwise acceptable)
represent U.S. soils that are of limited relevance to proposed pesticide use areas (resulting in the use of the data only for site specific representation if the study is otherwise acceptable)
do not represent any U.S. soils that are relevant to proposed pesticide use areas (resulting in the rejection of the data for use in the risk assessment process).
EFED science staff (and contractors) should use the following criteria to evaluate whether to use a study conducted with foreign soils:
EFED science staff (and conductors) should have soil classification information in registrant submitted fate studies. If this information is not available, adequate data such as soil profile description as well as physical and chemical properties of soils should be provided in the study in order to classify the study soils in accordance with the FAO soil classification (i.e., soil units) or equivalent U.S. Soil Taxonomy classification system. FAO Soil Units and equivalent classification under the U.S. Soil Taxonomy classification system are presented in Table 1.
The U.S. soils represented by the study soils should be considered relevant to and representative of the proposed/intended pesticide use areas in the U.S. This guidance (Figures 1-13) contains maps showing the distributions and brief descriptions of the major soils within the U.S.
For aerobic soil metabolism studies, the study (or an additional study) should include data obtained using U.S. soils and lasting for a sufficient duration to demonstrate similarity in degradation patterns between the foreign and domestic soils regardless of microbial population differences.
If these criteria are not met, the study is not acceptable and cannot be used alone to support risk assessment. In some cases, foreign soils that are representative of soils from specific regions of the U.S. may have limited relevance to other areas of the U.S. In this case, the data may be used to assess risk only in certain site-specific areas for a proposed pesticide use. In such cases, this should be clearly stated in the comments section of the Data Evaluation Records (DERs) and in the risk assessment.
| FAO Soil Units | U.S. Soil Taxonomy | Comments* |
|---|---|---|
| Acrisols | Ultisols | Distribution of Ultisols (Figure 3). |
| Andosols | Andepts | Soils derived from volcanic deposits. Limited to Northwest USA (Figure 9). |
| Arenosols | Psamments | Suborder of Entisols. Soils of coarse texture (Figure 14). |
| Cambisols | Inceptisols | Distribution of Inceptisols (Figure 5). |
| Chernozems | Borolls | Suborder of Mollisols. Mollisols that have a frigid, cryic, or pergelic soil temperature regime. |
| Ferralsols | Oxisols | No Oxisols in the continental USA. |
| Fluvisols | Fluvents | Suborder of Entisols. Recent alluvial soils. |
| Gleysols | Aquic suborders | Poorly drained soils. |
| Greyzems | Borolls | Suborder of Mollisols. Mollisols that have a frigid, cryic, or pergelic soil temperature regime. |
| Histosols | Histosols | Distribution of Histosols (Figure 11). |
| Kastanozems | Ustolls | Suborder of Mollisols. Mollisols from dry regions (Figure 15). |
| Lithosols | Lithic Subgrups | Soils of <10cm depth over hard rock. |
| Luvisols | Alfisols | Distribution of Alfisols (Figure 2). |
| Nitosols | Ultisols and Alfisols | Base saturation dictates Soil Orders. Alfisols >35% Base saturation. Ultisols < 35% Base saturation. |
| Phaeozems | Udolls | Suborder of Mollisols from humid regions (Figure 15). |
| Planosols | No equivalent | Soils with a bleached and temporarily water-saturated topsoil. |
| Podzols | Spodosols | Distribution of Spodosols (Figure 8). |
| Podzoluvisols | Glossic, Great groups of Alfisols | Soils with glossic horizon. |
| Rankers | Lithic Haplumbrets | Shallow Inceptisols soils with umbric A horizon. Umbric is a diagnostic epipedon similar to mollic but more acidic. |
| Regosols | Ortherents, Psamments | Suborders of Entisols. Distribution of dominant Suborders of Entisols (Figure 14). |
| Rendzinas | Rendolls | Suborder of Mollisols. Mollisols that contain CaCO3 equivalent of >400 g kg-1 within or immediately below the Mollic epipedon. (Figure 15). |
| Solonchaks | Salic Great Group | Accumulation of secondary silica. |
| Solonetz | Natric Great Group | Soil with Agrillic horizon with >15% saturation with exchangeable sodium. |
| Vertisols | Vertisols | Distribution of Vertisols (Figure 10). |
| Xerosols | Mollic Aridisol | Aridisols with Mollic horizons. |
| Yermosols | Aridisols | Distribution of Aridisols (Figure 7). |
* The Glossary of Soil Science Terms has a comprehensive glossary of soil science terms to search and browse.
Example of the Use of Limited Soil Taxonomy Data in Submitted Studies
Although the soil order (under U.S. Soil Taxonomy) may not be clearly identified in a submitted study, there may be information available to easily determine the soil order. Each name of an order contains a formative element, as listed in Table 2. For example, in the order name "Entisol," the formative element is ent. In the name "Aridisol," it is id. These formative elements are used as endings for the names of suborders, great groups, and subgroups. The suborder of Entisols that has aquic conditions throughout is called Aquents (L. aqua, water, plus ent from Entisol). The suborder of Entisols that consists of very young sediments is called Fluvents (L. fluvius, river, plus ent from Entisol). Thus, if the taxonomical classification of the soil is given, a reviewer may determine the soil order from that information. For example, a soil with the taxonomical classification "Fluvaquentic Haploxeroll, coarse-loamy, mixed, thermic" can be determined to be of the soil order "Mollisol" based on the -oll in the subgroup name Haploxeroll. A soil with the taxonomical classification "Typic Hapludalf, fine loamy, mixed, mesic" can be determined to be of the soil order "Alfisol" based on the -alf in the subgroup name Hapludalf. For more information concerning U.S. soil taxonomy, refer to the following web site: http://soils.usda.gov/technical/classification/orders/.
| Name of order | Formative element in name | Derivation of formative element |
|---|---|---|
| Alfisols | Alf | Meaningless syllable |
| Andisols | And | Modified from ando |
| Aridisols | Id | L. aridus, dry |
| Entisols | Ent | Meaningless syllable |
| Gelisols | El | L. gelare, to freeze |
| Histosols | Ist | Gr. histos, tissue |
| Inceptisols | Ept | L. inceptum, beginning |
| Mollisols | Oll | L. mollis, soft |
| Oxisols | Ox | F. oxide, oxide |
| Spodosols | Od | Gr. spodos, wood ash |
| Ultisols | Ult | L. ultimus, last |
| Vertisols | Ert | L. verto, turn |
Figures
Figure 1. Distribution of major soil orders (Larger Version of Map)
Figure 2. Distribution of Alfisols.
Alfisols
These soils have well developed horizons (layers) and a base saturation of 35% or greater. They typically have an ochric epipedon (surface layer), but they may have an umbric epipedon. They may also have a petrocalcic horizon, fragipan, or duripan. These soils are usually formed under forest or savanna vegetation.
Figure 3. Distribution of Ultisols
Ultisols
These soils have a horizon that contains appreciable amounts of translocated silicate clay (an argillic or kandic horizon) and few bases (base saturation less than 35 percent). Base saturation in most Ultisols decreases with depth. Ultisols are typically weathered and acid soils, and the nutrients are often concentrated in the upper few inches.
Figure 4. Distribution of Mollisols.
Mollisols
These soils have a dark colored surface horizon and are base rich. Mollisols characteristically form under grass in climate that has moderate to pronounced seasonal moisture deficit. They are commonly found on the steppes of Europe, Asia, North America, and South America.
Figure 5. Distribution of Inceptisols.
Inceptisols
These soils typically occur in humid and subhumid regions with altered horizons. Inceptisols usually have lost bases or iron and aluminum but have retained some weatherable minerals. They do not have an illuvial horizon enriched with either silicate clay or with an amorphous mixture of aluminum and organic carbon. The Inceptisols may have many kinds of diagnostic horizons, but argillic, natric, kandic, spodic, and oxic horizons are excluded.
Figure 6. Distribution of Entisols.
Entisols
These soils are sandy and have little or no evidence of development of pedogenic horizons. Many Entisols have an ochric epipedon (surface layer) and a few have an anthropic epipedon. Although Entisols are shallow and not well developed, they are commonly found in farm land throughout the world.
Figure 7. Distribution of Aridisols
Aridisols
Aridisols are soils that develop in very dry environments. Because of limited rainfall and high temperature, soil water tends to migrate in these soils in an upward direction, and gypsum, salt, and calcium carbonate often accumulate in the surface layer. These soils are too dry to support mesophytic plants. Aridisols commonly occur in the desert environment.
Figure 8. Distribution of Spodosols
Spodosols
In these soils, amorphous mixtures of organic matter and aluminum, with or without iron, accumulate in the B horizon. In undisturbed soils, there is normally an overlying eluvial horizon, which is generally gray to light gray in color. Most Spodosols have little silicate clay. The particle-size class is mostly sandy, sandy-skeletal, coarse-loamy, loamy, loamy-skeletal, or coarse-silty.
Figure 9. Distribution of Andisols
Andisols
Andisols are light textured volcanic soils that contain glass and poorly crystalline colloidal materials, including allophane, imogolite, and ferrihydrite (andic properties). In the United States, most Andisols occur around the Pacific Northwest and in Hawaii.
Figure 10. Distribution of Vertisols
Vertisols
These soils have a high content of expending clay and may have deep wide cracks at some period of time in the year. Vertisols shrink when drying and swell when wet. These soils are naturally fertile but difficult to cultivate for crop production.
Figure 11. Distribution of Histosols
Histosols
These soils contain a high percentage of organic matter and are commonly called bogs, moors, or peats and mucks. A soil is classified as Histosols if it does not have permafrost and is dominated by organic soil materials.
Figure 12. Distribution of Gelisols
Gelisols
These soils have permafrost and/or gelic materials within 100 cm of the soil surface, and permafrost within 200 cm of the surface. Gelic materials are mineral or organic soil materials that have evidence of cryoturbation (frost churning) and/or ice segeration in the active layer (seasonal thaw layer) and/or the upper part of the permafrost. In the United States, Gelisols occur predominantly in Alaska.
Figure 13. Distribution of Oxisols
Oxisols
These soils typically occur in the tropical and subtropical regions. They commonly occur on gentle slopes with stable landscape. Oxisols are mixtures of quartz, kaolin, free oxides, and organic matter. For the most part, they are nearly featureless soils without clearly marked horizons. Differences in properties associated with depth are so gradual that horizon boundaries are generally arbitrary.
Figure 14. Suborders of Entisols
Figure 15. Dominant Suborders of Mollisols
References
FAO-UNESCO, 1978. Report on the Agro-Ecological Zone Project. Food and Agriculture Organization and United Nations Educational, Scientific and Cultural Organization, World Soil Resources Report 48, Rome, Italy.
FAO-UNESCO, 1987. Soil of the World. Food and Agriculture Organization and United Nations Educational, Scientific and Cultural Organization, Elsevier Science Publising Co. Inc., New York, NY.
Riepert, F. and D. Felgentreu. 2002. Relevance of soil storage to biomass development, N-mineralization and microbial activity using the higher plant growth test, ISO 11269-2, for testing of contaminated soils. Appl. Soil Ecology: 20:57-68.
Soil Survey Staff, 1999. Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys. U.S. Natural Resources Conservation Service. USDA Handbook #436. Washington D.C.
Wild, A. Russell's Soil Conditions and Plant Growth. 11th Edision. P. 824. Longman and Scientific and Technical, New York, NY.
URLs.
German Standard Soils
(http://www.lufa-speyer.de/soil_eng.html)
Keys to Soil Taxonomy (http://soils.usda.gov/technical/classification/tax_keys/)
Distribution Maps of Dominant Soil Orders (http://soils.usda.gov/technical/classification/orders/)
Glossary of Soil Science Terms
(http://www.soils.org/sssagloss/)
The Twelve Soil Orders
(http://soils.ag.uidaho.edu/soilorders/orders.htm)
Soil Orders
(http://www.soils.wisc.edu/courses/SS325/soilorders.htm#alfisols )