CRA

What Is Maximum Residue Limit (MRL) and How to Set MRLs for Pesticides

Little Pro on 2019-07-03 Views:  Update:2019-07-03

Maximum Residue Limits (MRLs) are defined as the maximum concentration of pesticide residue (expressed as mg of residue per kg of food/animal feeding stuff, mg/kg) likely to occur in or on food as a result of the use of pesticides according to good agricultural practice (GAP) and product label recommendations.

How to Set MRLs for Pesticides

When a pesticide has been registered on a particular crop, the MRL for the pesticide in/on the crop is usually set at a value determined from supervised field residue trials. However, if a pesticide has not been approved for use on a crop, the MRL can be set at the limit of determination (LOD). In EU, the default lowest LOD is 0.01mg/kg.

How to Use Field Residue Trials to Set MRLs

If you get 8 independent residue values or more from supervised field trials, you can use the internationally accepted OECD MRL calculator to calculate proposed MRLs. The proposed MRLs become enforced MRLs only after they have been evaluated and approved by authorities.

The calculator distinguishes fully censored residue datasets (sample sets with all measurements below one or several limits of quantification LOQ) from not fully censored datasets (datasets with at least one measurement at or above the LOQ of the corresponding analytical method).

For fully censored datasets, the MRL proposed by the calculator  is the level of the highest LOQ present in the dataset

For not fully censored datasets, the maximum of three calculated values below is put forward as the MRL proposal by the calculator.

  • Highest residue
  • Mean + 4 * SD (standard deviation)
  • 3 * Mean * CF (correction factor: 1~2/3)

The table below shows you how to report calculated MRLs, Supervised Trials Median Residue (STMR) and Highest Residue (HR) from a given residue trial dataset. 

Region

Crop

Outdoor /
Protected

Residue Dataset

(mg/kg)

MRL
Calculated

(mg/kg)

MRL
Rounded

(mg/kg)

STMR

(mg/kg)

HR

(mg/kg)

EU

Oilseed rape

Outdoor

0.04, 0.05, 0.05, 0.05, 0.07, 0.07, 0.07, 0.07, 0.08, 0.09, 0.12, 0.12, 0.13, 0.16, 0.17, 0.20, 0.21, 0.21, 0.37, 0.48, 0.72

0.833

0.9

0.12

0.72

We will talk about supervised trials median residue (STMR) and highest residue (HR) in our next article.

MRLs and Dietary Risk Assessment

In dietary risk assessment, MRLs are used to calculate the theoretical maximum daily intake (TMDI) using the World Health Organization (WHO) European Diet or national dietary information as the basis for their calculations.

TMDI = Σ MRLi x Fi

where

  • MRLi = Maximum Residue Limit (or national maximum limit) for a given food commodity
  • Fi = National consumption of that food commodity per person

If the theoretical maximum daily intake exceeds the proposed Acceptable Daily Intake (ADI), proposed MRLs will be rejected. 

Reference

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 Tags: Topics - CRAToxicology and Health Risk Assessment

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