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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

Questions?

Thank You