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Improving Control Systems in Thailand for Plant and Plants Products Intended for Export to the
European Union co-funded by the European Union and
Thai Department of Agriculture
Preharvest Use of Pesticides - Training of Trainers
Workshop
What are MRLs and How are they Determined?
George Fuller, Ph.D.
Asia Food Solutions
Outline
• What are MRLs
• How are they established?
• Dietary Safety
• Practical Considerations
• Global Assistance
What is a MRL?
• Maximum residue limit (MRL) - maximum
concentration (mg/kg) of a residue that is
legally permitted1 or recognised as
acceptable in, or on, a food, agricultural
commodity or animal feedstuff.
• Also known as LMR, Tolerance, WHL, Import
Tolerance1 – resulting from the use of the pesticide according to good agricultural practice (GAP)
What is a MRL?
• MRLs indicate proper use of GAP and are
important in trade in agricultural commodities
• Residues resulting from the use of the
product at the GAP must be shown to be safe
to the consumer, but the MRL is not a safety
limit.
• Residues above the MRL can still be safe.
How are MRLs
Established?
Residue Definition
Supervised residue trials – GAP
(locally set pest pressures
and conditions)
Method of calculation
– range of data
– statistical analysis
– expert judgementDietary intake assessment to
confirm consumer safety
MRL
How are MRLs
Established?
• Scientists must show what happens to a
pesticide in and on the plant.
• The final breakdown products tell them how
to define the residue and what to look for.
Residue Definition
How are MRLs
Established?
• Researchers apply the pesticide under
realistic field conditions and then analyze
the crops to find out how much pesticide is
there.
Supervised residue trials – GAP
(locally set pest pressures
and conditions)
How are MRLs
Established?
• In many cases residues can be found at
VERY low levels, usually at the part per
million (ppm) or billion (ppb) level.
• A typical limit of detection would be 0.05
ppm (50 ppb)
How Much is a PPB?
• If a football field was covered with rice 4.5
meters high, a part per billion would be a
single grain of that rice
How are MRLs
Established?
• Usually field trials provide a range of residue
numbers and experts will analyze all the data
to determine what number best represents the
maximum that could be expected if GAP is
followed
Method of calculation
– range of data
– statistical analysis
– expert judgement
How are MRLs
Established?
• Experts calculate how safe the proposed
MRL would be for consumers
Dietary intake assessment to
confirm consumer safety
Dietary Safety
Hazard Exposure
Risk
Risk = (hazard, exposure)
Residue in food and intake
Of that foodResults of studies
with laboratory
animals
Dietary Exposure
MRLs (Maximum Residue Levels)
Residues from Supervised Field
Trials
Processing Studies
Monitoring Data
Market Basket Surveys
Dietary Safety
A factor of at least
100 is applied
between NOAEL
and ADI/ARfD
ADI
MRL
ARfD
Increasing
Residue Amount/
Increasing Risk
Zone 3: ADI and/or ARfD are significantly exceeded, meaning there
may be a human health concern. Given the safety margins
incorporated into the ADI and ARfD, case-by-case assessment is
appropriate, and if necessary steps to prevent the sale of the
crop/commodity should be taken.
Zone 2: MRL exceedance, not legal for trade but safe for human
health. Case-by-case analysis and appropriate steps to ensure future
compliance with MRLs should be undertaken.
Zone 4: NOAEL is exceeded, meaning there is a human health
concern. Immediate steps to prevent the sale of the
crop/commodity have to be taken.
Actual residues are
typically below the MRL,
i.e. in this range
LOAEL
MRL: Maximum Residue Level (Maximum contents of a pesticide residue to be legally
permitted in or on food commodities)
ADI: Acceptable Daily Intake (Estimate of the amount of a substance in food, which can
be ingested daily over a lifetime by humans without appreciable health risk)
ARfD: Acute Reference Dose (Estimate of the amount of a substance in food, which can
be ingested in a single meal by humans without appreciable health risk)
NOAEL: No Observable Adverse Effect Level (The greatest concentration of an agent,
that causes no detectable adverse alteration of morphology, functional capacity, growth,
development or lifespan of the target.
LOAEL: Lowest Observable Adverse Effect Level (similar to NOAEL, but where an effect
is seen)
Zone 1: MRL
compliance, legal for
trade, safe for human
health. The vast
majority of measured
samples fall in this zone.
Practical
Considerations
Exceeding the MRL
By Chance
• ‘Unlucky’ farmer exceeds MRL even
though GAP was followed
– Unusual conditions
– Chance occurrence of sampling and analysis
By Misuse
• Product not applied using GAP or not a
registered use of the product
Practical
Considerations
• MRLs can and do differ globally
– Different countries can have different GAP
– Different countries look at the same data in different ways
• Exporters need to know MRLs in destination
countries
MRLs for
Apples
Global Assistance
• CODEX Alimentarius Commission
– Proposes MRLs as international standards for
trade
– Accepted by most countries, esp. Japan
– Not necessarily accepted by EU
• Global Minor Use effort
– Works through CODEX
– Looking at crop groupings to maximize impact
of residue data
Global Assistance
• USDA/STDF Program to conduct minor
use residue trials in tropical areas
– ASEAN proposal has been submitted
– Could start in 2012 with results in 2015
• Global Residue Trial
– Study to find out if doing trials under the same
conditions in different countries and climates
results in different residues.
– Can be used to apply residue data on a global
basis
Useful Sites
• CODEX
http://www.codexalimentarius.net/mrls/pes
tdes/jsp/pest_q-e.jsp
• EU
http://ec.europa.eu/sanco_pesticides/publi
c/index.cfm
• US and international
http://www.mrldatabase.com