NRCS National Agricultural Pesticide Environmental Risk Analysis.....NAPRA
The Indiana Statewide NAPRA Effort is a Cooperative Project which involves:
The USDA-Natural Resources Conservation Service , specifically
(National NAPRA Team)
Indiana Dept. of Environmental Management (IDEM)
Office of the Indiana State Chemist (OISC).
The Indiana State Conservationist
Purdue University Cooperative Extension Service
Conservation Technology Information Center
Purdue University Agronomy Department
Purdue University Agricultural and Biological Engineering Department
This page contains a general explanation of NAPRA, followed by an extensive description of the NAPRA process
and a list of online resources.
NAPRA Indiana Homepage Information Index:
- NRCS Three-Tiered Pesticide Environmental Risk Screening
- Tier One SPISP Example
- Tier Two NAPRA Example
- Summary
- Online Resources, Web Pages and Data Browser
- Ready to go? Navigation Buttons
- Agronomy Department Contact Person
General Discussion of NAPRA
Researchers in the Departments of Agronomy and Agricultural & Biological Engineering are currently studying
a Natural Resources Conservation Service (NRCS) model which will help the farmer and county extension agent choose
the best practice to prevent pesticide loss, using site-specific information.
This model, called NAPRA, uses 30 to 50 years of climate and rainfall data along with soil and crop characteristics
specific to the local area to generate a 30 year range of probabilities for pesticide loss using specific practices
on that soil.
The approach which the model takes is to run a standard scientific leaching model, GLEAMS, over and over, using
each year's weather for the last 30 years, and all the other listed input data, to calculate the chance that a
particular pesticide would have leached into groundwater from this soil, had conditions been all the same. This
is not an attempt to say that this specific farm produced some contaminant in a certain year. The answers are in
probabilities. For example, it might report that for this field one tillage practice with corn has a 2 %
chance of atrazine leaching in detectable amounts over the next 20 years, but a different tillage practice with
corn would have a 0.05% chance of leaching. The county agent and farmer could compare yields, labor, and equipment
costs of the two methods against the modeled probability of contamination when picking a management strategy. The
model can calculate probability of exceeding any specified limit for a wide range of agricultural chemicals, making
it a very flexible tool.
Return to Information Index
A three-tiered environmental risk screening process.
Following text from class material created by Joseph K. Bagdon and the NAPRA Team, USDA-NRCS, Amherst
MA.
Some emphasis added by Purdue Agronomy segment of INDIANA NAPRA Team.
NRCS Pesticide Environmental Risk Analysis
Pesticides have been found in surface and groundwater nationwide. USDA continues to be very concerned about
nonpoint source contamination due to normal agricultural practices. Our goal is to minimize pesticide risk
to the environment. To accomplish this, we must help producers to understand all of the environmental risks associated
with their pesticide management decisions.
- Quantifying the environmental benefits of alternative management strategies is the key. NRCS has delivery
tools:
- SPISP - Soil/Pesticide Interaction Screening Procedure and
- NAPRA - National Agricultural Pesticide Risk Analysis,
which can be used to evaluate the potential risks of off-site pesticide movement. Results can be used to formulate
water quality best management practices.
- Our charge is to help farmers choose pesticide management alternatives that reduce hazardous pesticide losses
not only to drinking water, but to all components of our ecosystem.
NRCS Three-Tiered Pesticide Environmental Risk Screening
Tier One decision aid support is provided by the NRCS Soil/Pesticide Interaction Screening Procedure (SPISP).
SPISP evaluation is based on pesticide and soil properties that influence environmental fate. It screens
pesticide/soil combinations into two classes:
- those that result in a low risk of off-site pesticide movement
- those that need further evaluation.
SPISP has two main functions:
- (1) to educate field staff and agricultural. producers about the influence of soil and pesticide properties
on the fate of pesticides in the environment and
- (2) to identify areas that have significant potential for off-site pesticide movement, so we can work there
first to maximize environmental risk mitigation with our limited resources.
Tier Two decision aid support is provided by the automated National Agricultural Pesticide Risk Analysis (NAPRA)
process. NAPRA utilizes the USDA-ARS environmental fate computer model GLEAMS (Groundwater Loading
Effects of Agricultural Management Systems, Knisel, 1994).
Probabilities of exceeding pesticide mass loadings and concentrations are developed by running 30 to 50 years
of climate data. Annual pesticide concentrations in runoff and percolate, as well as yearly four-day maximum percolate
and runoff concentrations are developed.
Tier Two NAPRA has been designed to provide further evaluation when it is called for by Tier One SPISP
screening. NAPRA results are designed to help quantify the potential environmental benefits of management
alternatives.
Tier Two NAPRA analysis is focused on generic management scenarios and how pesticide losses are affected
by management under the climatic conditions of the region being studied. Results are probability based and consider
both the off-site movement of pesticide and its toxicity to non-target species.
Tier Three analysis is site specific. It can also be performed with NAPRA software. At this Tier
Three level, generic (Tier Two) inputs are replaced by individual producers' filing records and field measured
soils data. The cost of acquiring this detailed data may limit the implementation of Tier Three analysis. It should
be targeted to situations where there is a high level of environmental concern and Tier Two generic scenario analysis
indicates a high level of risk for all viable alternatives.
The NRCS three-tiered pesticide risk analysis process is summarized in Table 1.
Table 1: NRCS Three-Tiered Pesticide Environmental Risk Screening Technology
- Tier One: SPISP- Pesticide Properties and Soil Properties.
- Tier Two: NAPRA- Generic Scenarios- add Pesticide toxicity, Regional Climate and Generic Cropping and Management
Practices.
- Tier three: NAPRA Field Specific Scenarios- Add local Climate and Producer Specific field Data for All Inputs
SPISP and NAPRA technology cannot be effectively implemented without close cooperation with the
Cooperative Extension Service, independent crop consultants and agribusiness representatives. Their technical expertise
in alternative management practices, efficacy, and economic considerations, will all be essential to the development
of sound pesticide environmental risk analysis. They can also provide outlets for the risk analysis information
and reinforcement of its value.
Without academic and private sector "buy-in" growers will be reluctant to accept and utilize the new
technology. In addition, strong educational programs must accompany this three-tiered environmental risk screening
process to prevent its misuse. An example of this process is presented for Lancaster County, Pennsylvania.
Return to Information Index
Tier One SPISP Example:
Table 2 provides pesticide parameter data and SPISP II ratings for four common corn herbicides. All of
these herbicides have physical and biochemical properties that make them relatively mobile in water. For these
particular pesticides, differences in Koc and solubility are not as sensitive as soil 1/2 life. Atrazine and Metolachlor
have higher mobility ratings than Cyanazine and Alachlor primarily due to differences in their soil 1/2 lives.
Table 2: SPISP II Pesticide Ratings
|
Pesticide
|
Koc
|
Solubility (PPM)
|
Soil 1/2 life (days)
|
Leaching (LCH)*
|
Solution (SOL)*
|
Adsorbed (ADS)*
|
|
Atrazine
|
100
|
33
|
60
|
1
|
1
|
2
|
|
Cyanazine
|
190
|
170
|
14
|
2
|
2
|
3
|
|
Alachlor
|
170
|
240
|
15
|
2
|
2
|
3
|
|
Metolachlor
|
200
|
530
|
90
|
1
|
1
|
2
|
*1= large, 2= medium, 3= small, 4 = extra small (leaching only)
The SPISP process requires analysis of both pesticide properties and soil properties. For this example,
we will use Pennsylvania soils shown in Table 3.
Table 3: SPISP II Soil Ratings
|
Soil & Texture Class
|
K factor
|
O.M. %
|
depth of first layer
|
Hydro Group
|
Leaching (LCH)*
|
Solution (SOL)*
|
Adsorbed (ADS)*
|
|
Chester SIL
|
0.32
|
3
|
10
|
B
|
2
|
2
|
2
|
|
Colonie VFSL
|
0.24
|
2
|
10
|
A
|
1
|
3
|
3
|
|
Hagerstown SIL
|
0.32
|
3
|
10
|
C
|
3
|
1
|
1
|
*1= high, 2 = intermediate, 3 = low, 4 = very low (leaching only)
Pesticide and soil ratings combined in a matrix of all possible pesticide/soil combinations are shown in Table
4.
Table 4: Summary of SPISP II Ratings (Pesticide /Soil)
|
Pesticide
|
|
Chester SIL
|
|
|
Colonie VFSL
|
|
|
Hagerstown SIL
|
|
| |
LCH
|
SOL
|
ADS
|
LCH
|
SOL
|
ADS
|
LCH
|
SOL
|
ADS
|
|
Atrazine
|
1/2
|
1/2
|
2/2
|
1/1
|
1/3
|
2/3
|
1/3
|
1/1
|
2/1
|
|
Cyanazine
|
2/2
|
2/2
|
3/2
|
2/1
|
2/3
|
3/3
|
2/3
|
2/1
|
3/1
|
|
Alachlor
|
2/2
|
2/2
|
3/2
|
2/1
|
2/3
|
3/3
|
2/3
|
2/1
|
3/1
|
|
Metolachlor
|
1/2
|
1/2
|
2/2
|
1/1
|
1/3
|
2/3
|
1/3
|
1/1
|
2/1
|
The total of the pesticide and soil rating must equal 5 or more to result in a P (Pass), otherwise the rating
is E (Evaluate). Final ratings are displayed in Table 5.
Table 5: SPISP II Final Ratings
|
Pesticide
|
|
Chester SIL
|
|
|
Colonie VFSL
|
|
|
Hagerstown SIL
|
|
| |
LCH
|
SOL
|
ADS
|
LCH
|
SOL
|
ADS
|
LCH
|
SOL
|
ADS
|
|
Atrazine
|
E
|
E
|
E
|
E
|
E
|
P
|
E
|
E
|
E
|
|
Cyanazine
|
E
|
E
|
P
|
E
|
P
|
P
|
P
|
E
|
E
|
|
Alachlor
|
E
|
E
|
P
|
E
|
P
|
P
|
P
|
E
|
E
|
|
Metolachlor
|
E
|
E
|
E
|
E
|
P
|
P
|
E
|
E
|
E
|
P=Pass (low risk of off-site pesticide movement)
E=Evaluate (needs further evaluation)
With these particular soils, the majority of Soil/Pesticide combinations are rated E.
An E rating indicates that there is potential for off-site pesticide movement.
Further evaluation with NAPRA is warranted to determine if the movement potential is significant and
of toxicological concern.
By design, a P rating indicates a low probability of significant offsite pesticide movement with a high degree
of confidence. Further environmental risk screening (Tier Two) is not necessary, except in cases where a pesticide
is widely applied over an entire watershed and/or its toxicity very high. The mix of P's and E's can vary greatly
with different soil and pesticide combinations. However, it is unlikely that a Soil/Pesticide combination will
be rated P for both surface runoff and leaching.
Return to Information Index
Tier Two NAPRA Example:
Our goal is to refine the SPISP II evaluation with NAPRA. For this example, we will focus on.
a single soil, Chester silt loam, and one resource concern: a drinking water reservoir that receives water runoff
from a hypothetical field (pesticide losses associated with sediment are treated separately). NAPRA analysis
requires the specification of additional variables: climate, slope, slope length, tillage method, tillage direction,
amount of residue, pesticide application date, rate and method and pesticide toxicity. Pesticide toxicity's used
in this analysis are shown in Table 6.
Table 6: Pesticide Toxicities
|
Pesticide
|
Percolate (human) MCL/HA PPB
|
Percolate (fish) MATC PPB
|
Runoff (Human) MCL/HA PPB
|
Runoff (fish) MATC PPB
|
Sediment (fish) STV PPB
|
|
Atrazine
|
3
|
848
|
3
|
848
|
84,800
|
|
Cyanazine
|
1
|
288
|
1
|
288
|
54,720
|
|
Alachlor
|
2
|
37
|
2
|
37
|
6,290
|
|
Metolachlor
|
100
|
253
|
100
|
253
|
50,600
|
MCL = Maximum Contaminant Level, HA = Health Advisory,
MATC = Maximum Allowable Toxicant Concentration,
STV = Sediment Toxicity Value
NAPRA results in Table 7 are based on Lancaster, PA climate, 6% slope for 200 ft, moldboard/disk tillage
up and down the slope, no residue and a pre-emergent surface herbicide application on May 1. Pesticide application
rates used are the 1993 national averages in pounds of active ingredient per acre: atrazine 1. 16, cyanazine 1.
80, alachlor 2.00 and metolachlor 1.90. These rates are used only for illustrative purposes. Actual comparisons
between pesticides must be based on field specific efficacious rates.
Table 7: SPISP II versus NAPRA
|
Pesticide
|
SPISP II Solution Loss Potential
|
NAPRA Off-site Movement Potential
|
NAPRA Toxicity Exceedence Probability
|
|
Atrazine
|
E
|
38 %
|
38 %
|
|
Cyanazine
|
E
|
23 %
|
47 %
|
|
Alachlor
|
E
|
25 %
|
35 %
|
|
Metolachlor
|
E
|
79 %
|
<2 %
|
E = Evaluate (needs further evaluation)
Return to Information Index
NAPRA results are expressed as the percent probability of exceeding a specific concentration at the edge
of the field or below the bottom of the rootzone, in any one year. NAPRA Off-site Movement Potential is
based on the percent probability of each pesticide alternative to exceed the same concentration. In Table 7, the
"NAPRA Off-site Movement Potential" values are all based on atrazine's 3 PPB MCL.
The "NAPRA Off-site Movement Potential" is an intermediate result that provides a more refined
off-site movement potential than SPISP II, however, it does not consider variation in toxicity between pesticides.
The final step in the NAPRA process involves the use of each pesticide's toxicity to arrive at a final NAPRA
result.
The "NAPRA Toxicity Exceedence Probability" in Table 7 is based on each pesticide's individual
chronic human toxicity (MCL/HA) from Table 6.
Figure 1 illustrates the relationship between off-site movement potential and off-site risk based on
values reported in Table 7.
Table 8, "NAPRA Hazard Summary: Annual
Pesticide Loss", is based on the same variable inputs as Table 7, and additionally includes multiple management
scenarios. Results are reported for percolate, runoff and sediment, and hazards to both humans and fish are considered.
The NAPRA final results are " % Probability of Exceeding " MCL/HA, MATC or STV (the chance
of exceeding a specific concentration in any one year) and are specific to the following variables: Slope
= 6%, Organic Matter = 3.0 %, Soil= Chester Silt Loam, Climate = Lancaster Pa., Resource=
surface water, and Crop = corn, and all of the management practices listed.
Management practices: M/D is moldboard/disk, NT is no-till, RT is reduced tillage, LTD is up and down
the slope and PRE is pre-emergent. MCL, HA, MATC and STV are all acronyms for specific toxicity values that are
chosen based on the resource concern. Reading down the table through the four blocks of four herbicides, notice
how the relative risks (in the columns on the right) change as a function of management alternatives (in the columns
on the left).
Return to Information Index
Table 8 variables in the "Management Alternatives" descriptions are different in their details. Differences
in the results section between alternatives can be attributed to these variables.
Differences between individual pesticides under each management option (on Table 8) are linked to each pesticide's
physical and biochemical properties, and the application rates and toxicity's we chose for this example. Application
rates in this report are 1993 average application rates. Actual application rates are linked to soil type, climate,
pest pressure, etc. and vary widely.
-
Comparisons between pesticides would require the use of actual application rates.
Pesticide toxicity values used were reported in Table 6.
In this example, there are minimal off-site pesticide risks through percolation movement and relatively low
off-site pesticide risks through sediment movement. There are, however, relatively high off-site pesticide risks
in solution runoff, with some scenarios approaching a fifty percent chance of exceeding a pesticide MCL.
Exceedence probabilities are based on concentrations at the edge of the field and the bottom of the rootzone.
Exceedence probabilities in a water body, even if it was located at the edge of the field, would likely be considerably
smaller. Additional pesticide degradation and dilution may occur as the distance between the field and the water
body increases. However, even with the limitation that NAPRA does not model direct effects all the way into
a water body, reducing relative hazard at the edge of the field will usually result in similar decreases to hazard
within the water body.
Figure 2 illustrates management practice effects on the probability of annual pesticide solution runoff
to exceed each pesticide's MCL at the edge of the field. In this example, the best management alternative to protect
a drinking water reservoir from solution pesticide losses, is reduced tillage: residue management with shallow
herbicide incorporation as the only soil disturbance.
This alternative results in a two-thirds reduction in off-site pesticide risk compared to conventional
tillage with pre-emergent surface applied herbicide. In some cases, this reduced tillage alternative may conflict
with residue requirements that are in place for erosion control. Erosion can lead to sediment which impacts both
water quality and aquatic habitat.
The optimum solution for a particular ecosystem will change with different soils, climates and resource concerns.
The goal is to tailor the Resource Management System (RMS) components or Best Management Practices
(BMP's) to address all identified environmental risks to ground and surface water, without adversely affecting
other resource concerns including soil and air quality.
In Summary
NRCS Three-tiered Pesticide Environmental Risk Screening is designed to help protect our natural resources. SPISP
analysis can be used to target resource management planning efforts to areas that have the greatest potential for
off-site pesticide movement. SPISP results should be combined with water quality monitoring data to determine
where NAPRA analysis is warranted.
NAPRA adds local climate, management practices and pesticide toxicity, to the pesticide and soil properties
also considered by SPISP II. NAPRA evaluates the effects of alternative management strategies on
off-site pesticide risks. The goal is to develop RMS's and/or BMP's that are specific to the variability of our
natural resource concerns. To be effective, water quality management practices must be differentially applied based
on natural resource sensitivity.
Endquote from National NAPRA Team.
Return to Information Index
There are several online resources related to the NAPRA project.
As mentioned above, the homepage of the USDA-NRCS National NAPRA Team is at: http://www.wcc.nrcs.usda.gov/water/quality/frame/pestmgt.html
Agronomy Department Contact Person for this program is Professor
Ron Turco.
If you have questions or comments about this project, feel free to email me at: rturco@purdue.edu
Return to Information Index
Last Update: 05/08/00
These Indiana NAPRA pages constructed and maintained by: Larry Theller
I welcome your comments at:
theller@purdue.edu
