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The Fate of Pesticides in the Environment
Brent Clothier & Steve GreenEnvironment Group, HortResearch
Palmerston North
“Soils – the Final Frontier”A Special Section in Science (v 304, 11 June 2004),
Fiona Profitt (p1617) writes …
“Soils are a sponge for pesticides and other nasty compounds filtering down from the surface. Yet experts have only a sketchy idea of how the ground copes with this toxic trickle.
Regulatory agencies are crying out for data to improve assessments of environmental health risks, as there are literally tens of millions of chemicals in use out there.
The US Geological Survey and a handful of other agencies are planning an ambitious mission: a soil geochemical survey of all of North America”
Land intensification often requires irrigation, &a greater use of agrichemicals
What happens to the soil and the water underneath?
New Zealand Wine - Riches of a Clean Green Land
• Herbicides are used for weed control• Fungicides for mildew and botrytis cinerea• Insecticides for mealy bug, rollers & mites• CCA-treated posts are used as vine supports
The Push & Pull for Better Pesticide Practices
• The Push – The Resources Management Act 1990
Section 15 (1)No person may discharge any –
(a) Contaminant or water into water; or(b) Contaminant onto or into land in circumstances which mayresult in that contaminant entering water
• The Pull – EUREPGAP (Good Agricultural Practices)
3. Crop Protectionb. Choice of chemicals
#1 Is the product appropriate? Major Mustc. Advice on quantity & type of pesticide
#1 Recommendations been given by qualified advisors? Major Must
Where do the chemicals go?
(from Sarmah, Müller & Ahmad, 2004)
After landing on foliage– Degrade to harmless substances. Degradation enhanced by
sunlight & temperature.
– Wash off the foliage. Enhanced by rainfall soon after application.
– Remain on the foliage then theleaves fall and breakdown
– All of these processes are affected by pesticide chemistry
After arriving on the soil …• Degrade to harmless substances.
- Enhanced by short half-life, plus warm & moist soils
• Leach through the soil– Exacerbated by high rainfall, free-draining soils, low soil
organic matter, pesticides with little attraction to soil organic matter
• Accumulate in the soil– Long-lived pesticides strongly attracted to soil organic matter
Table A3. Pesticide profile and properties. KOC is a measure of pesticide mobility, T½ is a measure of pesticide persistence, and LD50 is a lethal dose for a 50% kill (see text for details). Pesticide ai Type Profile Koc Half life
T½ [d]
Oral LD50
[mg/kg rat]
Dermal LD50
[mg/kg rat]
Toxicity
amitrole H Non-selective control of annual & perennial weeds
200 3 > 1,100 >10,000 Harmful
buprofezin I Control mealy bug, scales and whitefly
1262 10 > 23,200 > 5,000 Low
captan F Broad spectrum control of fungal disease
202 2.5 > 9,000 ~ 10,000 Low
chlorothalonil F Broad spectrum control of fungal disease
1380 30 > 10,000 > 10,000 Low
chlorpyrifos I Broad spectrum control of most insects
6070 60 > 135 > 2,000 Poison
diquat H Contact herbicide to control annual weeds
10000 250 > 230 > 500 Poison
dithianon F A protectant fungicide 334 1 > 630 > 2000 Poison
Chemical properties of each pesticide
‘Risk’ depends on mobility & persistence. ‘Hazard’ depends on toxicity
fW
SPASMO Modelling Pesticide Fate: Predicting Where & How Much?
e(-KS. t)
e(-KF.t)
MP
MD
Resident massMA = appliedMF = on foliageMS = in soil
Mass lossesMP = volatilizationMD = degradationML = leachate
ML
Plants
fA
(1-fA)MA
MF
MS
Soil
fL
ML
Water
• Modelling to predict leachate
• Modelling to predict build-up
SPASMO Verified: Residues on Horotiu silt loam
Data from ESR [Murray Close]
0
5
10
15
0 200 400 600 800
Day
Pro
cym
ido
ne
[mg
/kg
]
data 0.1 m
Model 0.1 m
0
5
10
15
0 200 400 600 800
Day
Hex
azin
on
e [m
g/k
g]
data 0.1 m
Model 0.1 m
0
5
10
15
0 200 400 600 800
Day
Pic
lora
m [
mg
/kg
] data 0.1 m
Model 0.1 m
Soil residues at 0.1 m• leaching• degradation• exchange
0
0.2
0.4
0.6
0 200 400 600 800
Day
Hex
azin
one
[mg/
L]
data 0.2 m
Model 0.2 m
0
0.2
0.4
0.6
0.8
1
0 200 400 600 800
DayH
exaz
ino
ne
[mg
/L]
data 0.6 m
Model 0.6 m
0
0.05
0.1
0.15
0.2
0.25
0 200 400 600 800
Day
Hex
azin
on
e [m
g/L
]
data 1.5 m
Model 1.5 m
Hexazinone at depth• leaching• degradation• exchange
The SPASMO model – pesticide fate
Bentazone on pasture
Year1974 1975
Mas
s ap
plie
d [k
g-ai
/ha]
0.0
0.5
1.0
1.5
2.0
MTcropMTsoil
Mancozeb on onions
Year1974 1975
Mas
s ap
plie
d [k
g-ai
/ha]
0.0
1.0
2.0
3.0
4.0
MTcropMTsoil
Copper on onions
Year1974 1975
Mas
s ap
plie
d [k
g-ai
/ha]
0.0
10.0
20.0
30.0
40.0
MTcropMTsoil • Copper is strongly adsorbed and
does not degrade in soil. Continued use of will lead to accumulation
• Bentazone is highly mobile but rapidly degraded in soil. It has a low risk of leaching
• Mancozeb is strongly adsorbed, moderately persistent in soil. It has a low risk of leaching
Maize on a Taupo soil
Time [y]
1975 1980 1985 1990 1995 2000
Pest
icid
e Co
ncen
trat
ion
[mg/
L]
1e-8
1e-7
1e-6
1e-5
1e-4
1e-3
1e-2
1e-1
1e+0
MetribuzinMetolachlorCyanazine
(Report to Auckland Regional Council & Environment Waikato)
Modelling to assess the risks
Short term risk Elevated risk
The Growsafe® Calculator:
Pesticide Risk Reduction for Soil & Groundwater
A “Sustainable Farming Fund” project by the NZ Agrichemical Education Trust
involving the Hawke’s Bay Regional Council, Greater Wellington, EnvironmentWaikato, Tasman District Council, and Marlborough District Council.
Plus support from Gisborne District Council, Auckland Regional Council, Environment Canterbury, Otago Regional Council, Horizons Council, EnvironmentBay of Plenty, & the Northland Regional Council, that is 12 Local Authorities, plus
• Vegfed• NZ Winegrowers• Zespri International• NZ Pipfruit• NZ Fruitgrowers Federation• Arable Food Industry Council• NZ Avocado Growers• Summerfruit NZ• Agcarm
The Growsafe® Calculator:
Pesticide Risk Reduction for Soil and Groundwater
• Coverage over 12 regions in New Zealand• Some 31 crops considered• Spray diaries for 143 different pesticides• A total of 149 combinations of crop-by-region• Daily weather records over 30 years used• Some 5-8 named soils per region• A total of 28,399 SPASMO simulations, each 10,950 days
• Rankings of products in terms of
o Short-term leaching risko Long-term leaching risko Short-term soil build-upo Long-term soil buidl-up
• Impact of number of applications
Critical Values in Water Leaching @ 3m
• Few pesticides in the New Zealand Drinking Water Standard. If not …
• Our Critical Values developed fromØ Acceptable Daily Intake values from the Australian databaseØ Average person weight & their likely daily intake of groundwater (MoH)Ø Details provided in ‘Background Information’
Short & Long-Term Leaching Risks
Short-term, on 10% of (worst)days, Amitrole exceeds the CV. The next, Terbuthylazine is at ˜ 50% CV.
Long-term, on average over 30 years, nothing approaches 10% of CV. Terbuthylazine is the riskiest.
Impact of Soil Type on Leaching
On the stony Omahu gravels,if apples were grown, Terbumeton is a long-term risk
Just down the road, on a Twyford silt loam there is little leaching risk from ‘spray-diary’ usage
Bentazone on pasture
Year1974 1975
Mas
s ap
plie
d [k
g-ai
/ha]
0.0
0.5
1.0
1.5
2.0
MT cropMT soil
Mancozeb on onions
Year1974 1975
Mas
s ap
plie
d [k
g-ai
/ha]
0.0
1.0
2.0
3.0
4.0
MT cropMT soil
Copper on onions
Year1974 1975
Mas
s ap
plie
d [k
g-ai
/ha]
0.0
10.0
20.0
30.0
40.0
MT cropMT soil
• Copper is strongly adsorbed & does not degrade in soil.
• Bentazone is highly mobile but rapidly degraded in soil.
• Mancozeb is adsorbed & persistent in soil. The number ofapplications is critical
Soil Build-Up
Short & Long-Term Risks
Short & Long-Term Soil Build-Up of Pesticides
• Mancozeb, here applied 15 timesa season, will over the short-term,build-up in the soil.
• Because Mancozeb does not degrade quickly, it will continue to build-up. One application of copper poses a risk
Legacy Risks from Former Practices
• Mobility depends on Solubility and Koc (in solution, or sorbed to soil)
• Persistence depends on pesticide Half-life (degradation, leaching)
(SMF Project: Guidelines for the the Management of Sheep Dip Sites)
Dip Formulation
Solubility [mg/L]
Koc [L/kg]
half life [d]
AFR index
Lindane 7.000 1355 423 4.3
DDT 0.040 24000 3800 4.9
Arsenic 17000.000 100000 10000 5.4
Dieldrin 0.140 12000 1000 5.6
Diazinon 60.000 1520 39 6.8
Aldrin 0.027 17500 365 7.0
Cypermethrin 0.004 61000 36 10.5
∞
Year1950 1960 1970 1980 1990 2000
Soil
resi
dual
[mg/
m2 ]
0
200
400
600
800
1000
Arsenic Dieldrin Lindane Diazinon
Modelling to Assess Pesticide Fate
(SMF Project: Guidelines for the the Management of Sheep Dip Sites)
Dieldrin resident in soil
Year1950 1960 1970 1980 1990 2000
Die
ldri
n co
ncen
trat
ion
[mg/
m2 ]
0.001
0.01
0.1
1
10
100
1000
0.1 m0.2 m0.5 m1.0 m3.0 m6.0 m
Dieldrin• Movement to depth (still rising at 6 m after 40 yrs)• Some degradation
C12H8Cl6O
(SMF Project: Guidelines for the the Management of Sheep Dip Sites)
Modelling to Pesticide Fate
Tongatapu’sfresh water lenses
The Pesticide Problem… around the World
Tonga
A NZAID/EU project
• The fate of a pesticide is a result of a complex interaction of soil, crop, weather, & the pesticide properties, plus spray practices
• New tools are being developed to identify ‘at-risk’scenarios, current & legacy, that are likely to cause problems of leaching or accumulation
• These new tools could help users identify chemical alternatives & better practices that are more environmentally friendly
Summary: