Residues and Contaminants – How We Assess

Report from a day in the lab

Ellen Scherbaum


CVUA Stuttgart has been publishing its reports on pesticide residues in plant-based foods on the Internet since 2003. These reports have often occasioned commentary and sometimes requests that the results be presented in different formats. The processing of over two million datasets per year is complex, because many factors must be considered. We explain our approach below.




Pesticide residues or contaminants – what is what?

We analyze pesticide residues as well as contaminants. In distinguishing between the two, we adhere to the legal definition referred to in the legislative texts in the following Info Box.


Info Box

"Pesticide Residues"

Reg. (EC) No. 396/2005 (abbr: Reg. 396/2005):

Pesticide residues means residues, including active substances, metabolites and/or breakdown or reaction products of active substances currently or formerly used in plant protection products as defined in Article 2, point 1 of Directive 91/414/EEC, which are present in or on the products covered by Annex I to this Regulation, including in particular those which may arise as a result of use in plant protection, in veterinary medicine and as a biocide;


German Regulated Residue Levels (RückstandshöchstmengenV, RHmV):

The RHmV is the national regulation for areas not covered by Reg. 396/2005. This would include, for example, piperonyl butoxide (synergist) or DEET (repellent). MRLs are also valid for these substances and are included in the number of pesticide residues in our reports.


The term “residues” as found in our reports refers to substances that are used as/for

  • plant protection
  • plant storage protection
  • post-harvest treatment
  • biocide
  • repellent, etc.,

and that can end up in food. Plant protection is only one of different possible fields of application. These substances can be used against

  • insects (insecticide)
  • weeds (herbicide)
  • bakteria (bactericide)
  • fungi (fungicide)
  • snails (molluscicide) and
  • nematodes (nematicide).

These are the "…cides", and they belong to the general term of "pesticide“. Given their effectiveness, they are subject to a toxicological assessment and, for the protection of consumers, are assigned maximum levels for their residues in or on plants. Practically speaking, that means every substance listed under the EU’s "list of active substances“ is a pesticide in terms of VO 396/2005.


Valid here is the expression "once a pesticide, always a pesticide“, meaning that a current application need not exist (see definition in the Info Box). In such a case, our report would include the substance in the count of pesticide residues.


Info Box

"Contaminants": Council Regulation (EEC) No. 315/93 (abbr: Reg. 315/93):

Contaminant means any substance not intentionally added to food which is present in such food as a result of the production (including operations carried out in crop husbandry, animal husbandry and veterinary medicine), manufacture, processing, preparation, treatment, packing, packaging, transport or holding of such food, or as a result of environmental contamination.

Food containing a contaminant in an amount which is unacceptable from the public health viewpoint and in particular at a toxicological level shall not be placed on the market. Furthermore, contaminant levels shall be kept as low as can reasonably be achieved by following good practices at all the stages

Contaminants are not included in the "list of active substances“, and only individual cases have been assigned maximum levels. They are not counted as pesticide residues and, in accordance with Reg. 315/93, are subject to the minimization imperative.


For our reports that means such substances are assessed separately. They are not included in the number of pesticides per sample.


An example that frequently makes for discussion is chlorate, or perchlorate. Chlorate was previously categorized as a total herbicide; it is still included, therefore, in the scope of applications under Reg. 396/2005, even if the residues detected in food don’t stem from its use as an herbicide. Perchlorate is a different story. It is a contaminant from, e.g. fertilizer, and has never been used as a pesticide. Legally, and in our reports, chlorate is considered a pesticide and perchlorate not.


Internally, we have endlessly discussed whether we should redefine chlorate, in contrast to the legal definition for pesticides. But there are other cases where a substance then would have to be redefined as well, such as nicotine, when it comes from contamination via cigarette smoke, or hexachlorobenzene, when it results from contamination in the soil. With the pesticide definition the legislators wanted to avoid the burden of determining the origin of residues. The maximum levels are valid, regardless of where the substances originated. Thus, we adhere to the legal definitions in our reports; anything else would lead to more uncertainty and discussions.


Maximum residue level sum, according to Reg. 396/2005

A so-called MRL sum has been determined in Reg. 396/2005 for a whole string of pesticides. In these cases so-called relevant metabolites (degradation and conversion products) and, in other cases, also conjugates, are included in the regulated MRL. The insecticide fenthion is an example of an MRL sum. The maximum level is determined for the sum of fenthion, together with the metabolites fenthion sulfoxide, fenthion sulfone, fenthion oxon, fenthion oxon sulfoxide and fenthion oxon sulfon calculated as fenthion. If an MRL sum is defined for a particular substance the group only counts as one substance and only the sum amount is calculated for the averages. The MRL sums that were considered in 2016 are listed in Annex 1.


Special cases

Bromide is the degradation product of the fumigant methyl bromide. Bromide also exists in nature, however. If amounts greater than 5 mg/kg sample are detected, it can be assumed that methyl bromide was used. Thus, bromide is only counted as a residue when the amount is greater than 10 mg/kg (that means, considering an analytical uncertainty of 50 %, the value is verified above 5 mg/kg).


Dithiocarbamates are a group of fungicides that have a wide scope of applications. After hydrolysis they are determined as carbon disulfide, for which the maximum values are also defined. However, carbon disulfide also develops from phytonutrients in cabbages and papayas. Findings of dithiocarbamates in these matrices are thus not considered as residues in our reports.


For organic products – a different story altogether!

Usage of synthetic pesticides is not allowed in organic farming, according to COM Regulation (EC) No. 889/2008. As a consequence, no pesticides, or only traces thereof, are found in organic foods. As there are no special MRLs for organic foods alone, the orientation value of 0.01 mg/kg is used for assessments. If residue levels lie above this threshold, this would point to an illegal application, cross-contamination or the mixing of the product with conventional ware. In these cases we report the labelling of “organic” as being fraudulent. Our analyses and reports serve the purpose of determining to what extent the regulations for organic farming are adhered to, and whether the labelling of products as "organic“ is thereby legitimate.


In the reports of our analyses of organic foods, we distinguish between residues above and below the threshold of 0.01 mg/kg.


“Natural” pesticides that are permitted in accordance with legislation are seen as conformable to organic farming, and are listed separately. They are not calculated together with residues from synthetic pesticides.


Substances that end up in the sample due to contamination, such as chlorate, are handled in the same way. These situations are presented in a special manner, but are not characterized as violations of the regulations for organic farming.



Synthetic pesticides are commonly used in conventional farming. To protect consumers, Europe-wide valid MRLs have been established for these substances in ordinance Reg. 396/2005. In our reports all substances that fall under this ordinance are considered to be pesticide residues.

Contaminants that don’t fall within the area covered by Reg.396/2005 are calculated separately.

Analyses regarding organic cultivation are concerned with the determination of whether the regulations for organic farming are adhered to. These cases distinguish between chemical-synthetic pesticides that are not permitted for use in organic cultivation and naturally-occurring, permitted substances. Further, a threshold of 0.01 mg/kg is used for assessments. Only residues above this threshold value are considered conspicuous and are reported.


We are aware that, based on different questions and interests, another type of evaluation could be desirable. However, we need a consistent format so that the reports are comparable from year to year, and so that, for example, fruits are not evaluated differently from vegetables.



Annex 1: Substances and metabolites from 2016 that are included in the residue definition and are only included in the calculation as a sum
  Parameter included in the residue definition and analyzed
Abamectin Avermectin B1a
Avermectin B1b
8,9-Z-Avermectin B1a
Aldicarb, Sum Aldicarb
Amitraz, Total Amitraz
BTS 27271
Benzalkonium chloride, Sum (BAC) Benzyl dimethyl octyl ammonium chloride (BAC-C8)
Benzyl dimethyldecyl ammonium chloride (BAC-C10)
Benzyl dodecyldimethyl ammonium chloride (BAC-C12)
Benzyl dimethyl tetradecyl ammonium chloride (BAC-C14
Benzyl hexadecyl dimethyl ammonium chloride (BAC-C16)
Benzyl dimethyl stearyl ammonium chloride (BAC-C18)
Carbofuran, Sum Carbofuran
DDT, Sum DDE, pp-
DDT, pp-
DDD, pp-
DDT, op-
Dialkyl dimethyl ammonium chloride, Sum (DDAC) Dioctyl dimethyl ammonium chloride (DDAC-C8)
Didecyl dimethyl ammonium chloride (DDAC-C10)
Didodecyl dimethyl ammonium chloride (DDAC-C12)
Dieldrin, Sum Dieldrin
Dimethoate, Sum Dimethoate
Disulfoton, Sum Disulfoton
Endosulfan, Sum Endosulfan, alpha-
Endosulfan, beta-
Fenamiphos, Sum Fenamiphos
Fenthion, Sum Fenthion
Fipronil, Sum Fipronil
Flonicamid, Sum Flonicamid
Fosetyl, Sum Fosetyl
Phosphonic acid
Glufosinate, Sum Glufosinate
Heptachlor, Sum Heptachlor
Heptachlor epoxide
Malathion, Sum Malathion
Methiocarb, Sum Methiocarb
Methomyl, Sum Methomyl
Milbemectin Milbemectin A3
Milbemectin A4
Oxydemeton-S-methyl, Sum Oxydemeton-methyl
Parathion-methyl, Sum Parathion-methyl
Phorate, Sum Phorate
Phosmet, Sum Phosmet
Pirimicarb, Sum Pirimicarb
Prochloraz, Total Prochloraz
BTS 44595
BTS 44596
BTS 9608
BTS 40348
Pyrethrum, Sum Pyrethrin I
Pyrethrin II
Jasmolin I
Jasmolin II
Cinerin I
Cinerin II
Pyridate, Sum Pyridate
Quintozene, Sum Quintozene
Sethoxydim, Total Sethoxydim
Spirotetramat, Sum Spirotetramat
Spirotetramat, Ketohydroxy
Spirotetramat, Monohydroxy
Terbufos, Sum Terbufos
Tolylfluanid, Sum Tolylfluanid
Triadimefon u. Triadimenol Triadimefon
Triflumizol Triflumizol
Triflumizol Metabolit FM-6-1


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Report published on 10.07.2017 11:21:53