RESTRICTED
WORLD TRADE G/SPS/W/75
15August 1996
ORGANIZATION(96-3227)
Original: Spanish
COMMENTS ONTHE DEVELOPMENT AND APPLICATION OFRESIDUE
LIMITS TOFOODS INTRADE UNDER
WTO SPSPRINCIPLES
Communication from Argentina
Thepaper submitted byourAustralian colleagues (G/SPS/W/34), inaconcise yetdetailed
summary, isanexcellent description ofthetrade problems connected withchemical residues and
Argentina agrees thatthematters listed inparagraph 22,"Issues forconsideration", aretheonesthat
should betaken intoaccount insetting national residue limits.
With particular reference tothesecond subparagraph ofparagraph 22,wewould point out
that,inaddition togood agricultural practice intheuseofagricultural chemicals, account should be
taken -bytheimporting country -ofthechemical residues control planofthecountry exporting the
goods concerned. Such plans should notmerely detect cases above theMRLs theyhavesetineach
instance, butshould especially address theprocedures forcorrecting situations caused byimproper
useofagricultural chemicals andveterinary drugs. Thisinparticular supports everything clearly stated
byAustralia inparagraph 21.
Anamount above theMRL insome batches should notinitself, orroutinely, mean thatthe
foodshould beseized ordestroyed. Itismuch more effective toreport theproblem thathasbeen
detected totheofficial department concerned inorder toensure afollow-up totheinvestigation ofthe
origin oftheexcess ortheviolation.
Special plans forspecial markets maybeadopted byexporting countries soastoguarantee
thebuyer 'srequirements concerning non-use ofcertain substances thatareprohibited inthebuyer 's
market yetauthorized inthecountry oforigin.
Inviewoftheprovisions ofArticle 12:2oftheSPSAgreement, webelieve thatcoordination
andintegration between international andnational systems andapproaches should focus notonlyon
theapproval oftheuseoffoodadditives ortheestablishment oftolerances butalsoonthesurveillance
andcontrol plans inmember countries.
TheNational Animal Health Service considers thatitismore effective forpublic health to
establish measures tocorrect thecauses oftheproblem thansimply toseize ordestroy afood
consignment, something thatwould beappropriate onlyinexceptional cases.
Having regard totheimportance andalsothecomplexity ofthistopic, weattach theProgramme
setupasthemonitoring andsurveillance system under theArgentine Residue andHygiene Control
PlanforFoods ofAnimal Origin (CREHA).G/SPS/W/75
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SENASA -CREHA Plan
Residue andHygiene Control PlanforFoods ofAnimal Origin
Types ofSampling -Criteria forDecisions
Unbiased sampling ormonitoring
Objective: Toprovide annually nationwide schematic information onthepresence ofresidues or
micro-organisms ortoxins infoods orinspecific food-producing populations.
Sample size: Thisdepends ontwofactors:
(a) Thelevelofstatistical reliability: generally 95percent(internationally accepted value);
(b) therelative frequency orrateofcases ofunacceptable values intended tobedetected.
Thelatter depends ontherisktohuman health ofresidues ofagiven substance.
Generally speaking, there aretwocategories:
When thesubstance isprohibited or
notapproved (unknown toxicology): 0.1percent
When thesubstance ispermitted with
onlysome restrictions: 1percent
Obviously, itispossible todetermine intermediate categories, butthese areusually the
internationally applied andaccepted values.
Inthese terms, fordetection purposes thesample sizeis:
0.1percentrate: 3,000 samples ayear
1percentrate: 300samples ayear
Purposive sampling
Objective: Toprevent consumption ofcontaminated food. Thisentails ahighsampling ratioand,
basically, holding backinspected products untilacertificate ofanalysis isobtained withresults allowing
them tobereleased.
Points ofapplication andsample size
Theidealsampling ratiois,ofcourse, 100percent,inasmuch asitwould make for100percent
foodsafety.
Ifthisratioisapplied toallproducts, theprogramme isunlikely tobecompleted because:
- There aredifficulties withthecapacity toretain goods;G/SPS/W/75
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- thewarehousing costswould increase significantly, because refrigeration isnormally
needed;
- thehighcostofanalysis, ifnotconducted according toastatistical criterion, could
reach thepoint where, inthebreakdown ofthecostofthefood, theproduction
component would beminimal compared withthecontrol component;
- serious disruption ofthemarketing chain, owing toinevitable analysis delays.
Thisdoesnotmean itshould notbedone, thereby jeopardizing public health. Account should
betaken oftwomatters which mean that,evenwithahighlevelofhuman health protection, these
factors donothaveasignificant impact.
These twomatters maybesummed upasfollows:
(1) Toknow asaccurately aspossible thecharacteristics ofthepopulation liable to
contamination, soastoselect withmaximum precision thesizeofthesubpopulation
tosample;
(2) totakeimmediate corrective action withregard tothecauses ofunacceptable results.
Point (1)issimply donebythetaking ofsamples orrequests foranalysis designed toproduce
thegreatest amount ofinformation possible.
Thegreater theinformation, thegreater thenumber ofsubpopulations thatcanbedefined,
andthefewer thenumber ofcomponents foreachsubpopulation. Indeed, itisthenpossible toapply
100percentfrequency toasufficiently size-limited subpopulation.
However, although thesizeofthesampling subpopulation hasbeenreduced, thenumber of
samples fora100percentsampling ratiomaystillbetoohighandtoodifficult toapply, because of
thefactors mentioned above.
Ifpoint (2)isthenforcefully andeffectively applied andtherateofunacceptable values is
recalculated, theproportion ofsamples tobetaken maybereduced toavalue which affords thesame
levelofprotection asamonitoring programme. Itisessential foraction tobetaken immediately so
thatthetimeinwhich the100percentrateisapplied isasshort aspossible.
Calculations
Where Emeans Unacceptable cases ofamounts exceeding tolerances orpositive cases
N Thenumber ofelements inthepopulation monitored
M Thenumber ofsamples taken ofthatpopulation
Ns Thenumber ofelements ofthesubpopulation which willbethesubject
ofpurposive sampling
Ms Thenumber ofsamples taken ofthesubpopulation
Tc Thecritical rateofunacceptable cases forshifting frommonitoring to
purposive sampling
Tu Therateofunacceptable cases inthepopulation
Ts Therateofunacceptable cases inthesubpopulation
Atthegiven point, theresult willbeTu>Tc,thusshifting topurposive sampling, andit
ispossible from thedatainthesamples todefine aspecific subpopulation.G/SPS/W/75
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Obviously, alltheunacceptable cases must becontained inthesubpopulation and,insofar
asfurther cases emerge intherestofthepopulation, theymustbeincorporated inthesubpopulation,
which, ifnecessary, willhavetoberedefined forthepurpose.
Thismeans thatTucannot beestimated byE/M, since amuch higher number ofsamples is
taken ofthesubpopulation withproblems, andtheresult would thenbyverybiased.
Itshould beestimated by:
Tu=TsxNs/N
Where Tscanbeestimated by:
Ts=E/Ms
Even when monitoring cannot beusedtoestimate thepopulation rate,itshould beusedto
detect unacceptable cases thatmayoccur intherestofthepopulation.
However,theaimisunitretentionsamplingthatwillprovidethepublicingeneralwithprotection
thatisnotlessthanthemonitoring programme. Accordingly, theproportion ofuninspected unitsmust
benotmore thanTc.
Theamount ofcontaminated units inthesubpopulation is:
NsxTs
Ifapartofthese enter processing ordistribution facilities, inaproportion of,say,
K(0<K<1),and
iftheproportion heldbackforanalysis atsuchfacilities isP(0<P<1),
theamount ofcontaminated units reaching thepublic is:
NsxTsxKx(1-P) [I]
Thetotalamount ofunits reaching thepublic from thatsubpopulation is:
NsxK [II]
Thetotalamount ofunits reaching thepublic from theentire population is:
NxK [III]
Dividing [I]by[III]gives thefraction ofcontaminated units reaching thepublic, namely:
=Tsx(1-P)xNs/N
Where isthefraction ofcontaminated units reaching thepublic.
Ifthepopulation istobeafforded thesame protection asmonitoring, then:
=TcG/SPS/W/75
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With thiscondition, thesampling ratiois:
P=1-(Tc/Ts) x(N/Ns)
or
P=1-Tc/Tu
Itisevident thatforthesame value of(Tc/Ts), thesmaller thesizeofthesubpopulation, the
lower thesampling ratio.
Thisformula should beapplied if,andonlyif,thedistribution oftheunitsofthesubpopulation
affects alloftheconsumer public, inother words, theunitsareuniformly mixed withtheunitsofthe
restofthestatistical population. Otherwise, iftheunits ofthatsubpopulation aredirected towards
consumption byaparticular group ofconsumers, thefollowing could beconsidered:
P=1-Tc/Ts
Which istheresult ofdividing [I]by[II].