401. Dithiocarbamate fungicides (Pesticide residues in food: 1977 evaluations)

DITHIOCARBAMATE FUNGICIDES JMPR 1977

Explanation

Individual monographs were prepared on ferbam, maneb, nabam, thiram,
zineb and ziram by the 1965 and 1967 Joint Meetings (FAD/WHO, 1965,
1968), and on manoozeb by the Meetings of 1967, 1970 and 1974
(FAO/WHO, 1968, 1971, 1975). The latter monograph also contains data
relating to the other ethylenebisdithiocarbamates (EBDC) maneb,
metiram, nabam and zineb. Separate monographs on the dithiocarbamate
fungicides as a group were also prepared at the 1970 and 1974
Meetings.

At the 1974 Joint Meeting, recommendations were made for temporary
tolerances for ethylenediamine and ethylenethiourea (ETU) derived from
Mancozeb on a number of commodities, and the further work required was
indicated. The following monograph addendum reviews available
information on dimethyl- and ethylenebisdithiocarbamates. The
propylenebisdithiocarbamate propineb has not been evaluated previously
and is therefore the subject of a separate monograph.

EVALUATION FOR ACCEPTABLE DAILY INTAKE

DIMETHYL DITHIOCARBAMATES: FERBAM, ZIRAM, THIRAM

The dimethyl dithiocarbamates possess similar metabolic and
toxicological potential where structures are similar. Thus, ferbam and
ziram were considered to be sufficiently alike to be grouped together.
The concerns relating to reactions with nitrite to form nitrosamines
and the potential for teratogenicity expressed by previous meetings
were considered. The present Meeting determined that an ADI for humans
could be established.

In the case of thiram, the difference in structure was sufficient to
warrant separate consideration. Thiram is also teratogenic at high
dose levels. In addition, data indicated that a diet supplying 0.015
mg thiram daily to rats resulted in weight loss, nervous disturbances
and severe anaemia. These data were available in summary form only. No
haematological data were available to the Meeting. Since in other
studies much higher dose levels did not result in significant weight
gain changes, the Meeting determined that the no-effect level should
be derived from the more extensive data available in a long-term
study. However, concerns relating to haematology were deemed to
require investigation and, hence, a temporary acceptable daily intake
for humans was established for this compound.

TOXICOLOGICAL EVALUATION

(a) FERBAM

Level causing no toxicological effect

Rat: 250 mg/kg in the diet, equivalent to 12.5 mg/kg bw

Dogs 5 mg/kg bw

ESTIMATE OF ACCEPTABLE DAILY INTAKE FOR HUMANS

0-0.02 mg/kg bw

(b) ZIRAM

Level causing no toxicological effect

Rat:250 mg/kg in the diet, equivalent to 12.5 mg/kg bw

Dog: 5 (mg/kg bw)/day

ESTIMATE OF ACCEPTABLE DAILY INTAKE FOR HUMANS

0-0.02 mg/kg/bw

Level causing no toxicological effect

Rat: 48 ppm in the diet, equivalent to 2.5 mg/kg bw

Dog: 5 (mg/kg bw)/day

ESTIMATE OF TEMPORARY ACCEPTABLE DAILY INTAKE FOR HUMANS

0-0.005 (mg/kg bw)/day

ETHYLENEBISDITHIOCARBAMATES: NABAM, MANCOZEB, MANEB, ZINEB

(a) NABAM

Nabam is sodium ethylenebisdithiocarbamate. Like other fungicides of
this class, it decomposes and is degraded to ETU and ethylenediamine
(EDA). It was evaluated by previous Joint Meetings and a temporary ADI
for humans was allocated in 1974.

Nabam is the most acutely toxic of this class of compounds and is
goitrogenic. The Meeting was concerned at the relatively high acute
toxicity of this compound and as it was unaware of any work currently
in progress, it was unable to recommend an ADI for humans or to
recommend the retention of the existing temporary ADI for humans.

However, it is recognized that nabam is used in agriculture only in
conjunction with zinc sulphate to form zineb before spraying.

(b) MANCOZEB, MANEB AND ZINEB

The Meeting was aware of further work in progress and for this reason
decided to retain the existing temporary ADI for humans for a period
of two years at the present level of 0-0. 005 mg/kg. This ADI for
humans applies to mancozeb, maneb and zineb individually or as the sum
of any or all of these.

PROPYLENEBISDITHIOCARBAMATE: PROPINEB

See separate monograph on this compound.

RESIDUES IN FOOD AND THEIR EVALUATION

RESIDUES RESULTING FROM SUPERVISED TRIALS

Additional data from supervised trials involving several
ethylenebisdithiocarbamates ware available to the Meeting from several
sources; these are summarized in Table 1.

FATE OF RESIDUES

The requirements for further work on EBDC's published by the 1974
Joint Meeting included:

1. Residue studies in which both the ethylenediamine moiety and
ethylenethiourea (ETU) are separately determined.

2. Further studies on the fate of residues during the preparation and
processing of foods with particular reference to their conversion to
ETU.

Information concerning these requirements was made available to the
Meeting. It appears that the first requirement is not likely to be met
because of inadequacies established in the analytical method
previously used to determine the EBDC residues as ethylenediamine
(Anonymous, 1977). Observed deficiencies included, the occurrence of
variable but high 'blank' values, low recovery of ETU added to crop
materials, and progressively lower recoveries with time from milk.
Data from treated samples were therefore considered to be unreliable
and use of the method should be discouraged. The growth of interest in

TABLE 1. Residues of mancozeb, maneb and zineb found in
various crops in supervised trials

Pre-harvest Residues found (mg/kg)
Compound Crop interval (days) Range Mean Source

Mancozeb Apples 22-44 0.6-3.0 1.5 Anonymous 1977

28 - 3.1} IUPAC 1977
42 - 1.7}

Carrots - 0.1-0.2 0.1} Phillips et al.
- 0.2-0.7 0.5} 1977

Grapes 0-30 1.9-5.1 3.7 Canada 1977

Spinach - 0.9-2.5 1.8} Phillips at al.
- 24-123 54 } 1977

Tomatoes 3-5 0.3-1.6 0.7 Anonymous 1977

- 0.1-0.6 0.3} Phillips at al.
1.4-2.3 1.9} 1977

Wheat 28-47 0-0.4 0.15 Anonymous 1977
(grain)

Maneb Cantaloupes 1-5 0.4-2.3 1.1}
Cucumbers 1-7 0 1-0.68 0.3}
Potatoes 1-14 <0.1 <0.1} Pease & Holt
Summer squash 1-7 < 0.1-0.56 0.2} 1977
Tomatoes 1-7 0.35-4.0 1.6}

TABLE 1 (Continued)

Pre-harvest Residues found (mg/kg)
Compound Crop interval (days) Range Mean Source

7-14 0.47-0.83 0.6 Canada 1977

- 1.5-2.3 2.0 Phillips at al.
1977

Grapes 14 2.3-7.5 4.6} Montedison 1977
24 1.2-5.9 3.4}

Zineb Pears 21 - 1.0 Canada 1977

(Residues determined as CS₂ and expressed as parent compound)

ETU residues has also led to a renewed interest in the CS₂ evolution
methods should give a better measure of the sum of those compounds
present which might be converted to ETU. The improved ethylenediamine
method of Newsome (1974) is more effective in measuring EBDC residues
but it excludes ETU and other components of the residue mixture.

The requirement for information regarding conversion to ETU has been
responded to in an unusual manner. The current position regarding many
aspects of ETU has been reviewed by the Commission on Terminal
Residues of the Applied Chemistry Division of the International Union
of Pure and Applied Chemistry (IUPAC, 1977). Their Special Report
deals with analytical methods; the chemistry of ETU; the dynamics,
transformation and occurrence of ETU residues; and the effects of
cooking and processing food containing ETU residues. The following
conclusions were recorded:-

1. ETU occurs an a primary reaction product of the EBDC
fungicides.

2. ETU is present in commercial formulations in varying amounts
(0.02-2%). The amount increases on storage under warm and
humid conditions.

3. Environmental degradation (metabolism in plants, soils,
animals and water) of the EBDC fungicides also leads to ETU
formation.

4. There is no evidence for the persistence or bioaccumulation
of ETU residues in plants, soils or water, although ETU is
detected as a metabolite and accumulates in the thyroids of
animals.

5. Currently, there are several adequate methods for the
determination of ETU residues, however, there are no simple
procedures that are universally applicable.

6. Monitoring data confirm the frequent presence of EBDC
residues in or on raw agricultural crops treated using good
agricultural practices. Generally, residues of EBDC do not
exceed nationally recommended tolerances 1 - 7 PPM.

7. A substantial portion of the EBDC residue may be removed
from the raw agricultural crop following a simple washing
procedure. These procedures remove approximately from 30 -
90% of the residue.

8. Monitoring data confirmed the presence of ETU residues in or
on certain raw agricultural crops. Generally, these residues
were less than 0.1 ppm. most approaching the lower limits of
analytical detection (0.01 ppm).

9. ETU is found in most heat processed foods, where EBDC
residues were found prior to processing. Heat processing has
been shown to convert from 16 to 23% (weight basis) of the
EBDC residues to ETU. Consequently, the concentration of ETU
my be higher in processed foods than in the raw agricultural
products.

10. Current chemical data do not preclude the contained use of
EBDC fungicides in good agricultural practices.

These conclusions were endorsed by the FAC Panel of Experts.

The IUPAC Commission also made the following recommendations for
further action:-

1. That the acceptable average daily intake of ETU and EBDO
should be calculated immediately.

2. Analytical methodology for ETU and ETU-forming compounds
should be simplified to expediate monitoring programs.
Simple, rapid and specific methods are required. An
international collaborative study should be initiated.

3. Toxicological significance of residues reported in
monitoring data should be determined by competent
international bodies.

4. Further studies of the degradation and metabolism of EBDC
and ETU in crops and animals should be conducted.

5. Further data on the conversion of EBDC residues to ETU in
various food processing procedures should be developed.
Studies to minimize the formation of ETU during food
processing should be initiated.

These recommendations were discussed by the Joint Meeting and were
generally accepted; recommendation 5 in particular was endorsed.

EVIDENCE OF RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION

Some data on residues of dithiocarbamate fungicides found in Sweden
and the Netherlands were considered. The former data are summarized in
Table 2 (Winell, 1975). Residues were determined by CS₂ evolution
and expressed as zineb. Only results at 1.0 mg/kg or above are
detailed here; these represent 27 out of a total of 617 samples
examined. Data available from the Netherlands (1977) showed that of 13
samples of endive and lettuce examined, none exceed 2 mg/kg as zineb.
Analyses of 1031 samples of varied fruits and vegetables specifically
for thiram residues (Netherlands, 1977) showed only 14 instances in

which the national tolerance of 3.8 mg/kg was exceeded. Of these, 12
(out of 45 examined) were samples of strawberries (ranging from 4.2 to
14.6 mg/kg: the other two were one lettuce (out of 590) and one
currant sample.

TABLE 2. Dithiocarbamate residues (1.0 mg/kg or greater)
found in crops in Sweden, (Winell. 1975)

Crop Country Residue found (as zineb, mg/kg)

Apples USA 1.0
Banana (peel) Honduras 3.5
Cucumbers Netherlands 1.0, 1.2
Grapes Italy 1.0, 2.4
Lettuce Belgium 3.7
Netherlands 1.8, 9.9
Melon (peel) Israel 1.7
Peaches Italy 2.6, 2.7
Pears Australia 1.4
Italy 1.1, 1.2, 1.2, 1.4, 1.5, 2.5
Sweden 1.0, 1.0, 1.1
Potatoes Sweden 1.0, 1.0, 1.0, 1.3, 2.2

METHODS OF RESIDUE ANALYSIS

A gas-liquid chromatographic procedure for the determination of traces
of ethylenethiourea in fresh vegetables, fruits, milk and cooked foods
(Onley et al., 1977) has been successfully collaboratively studied
(Onley, 1977). The method is designed to determine ETU without
interference from ethylenebisdithiocarbamates and has been adopted as
an "Interim Official First Action" procedure. Two extraction
procedures are described, before and after a cooking process. The
cooking step is included to permit assessment of ETU residues which
could result from the conversion of EBDC fungicides that may also be
present on the raw commodities.

A new method which does not require the formation of a derivative of
ETU prior to gas chromatography has been proposed by Otto at al.
(1977). Plant material is extracted with methanol in the presence of
sodium ascorbate. After clean up by hexane:water partition, alumina
column chromatography of the aqueous phase and subsequent
dichloromethane water partition, the ETU is measured directly by GLC
with a flame photometric detector in the sulphur mode. A limit of
detection of 0.01 mg/kg is claimed.

APPRAISAL

Mancozeb and other ethylenebisdithiocarbamates (EBDCs) were considered
by the 1967, 1970 and 1974 Joint Meetings and further information had
been requested concerning the occurrence of ethylenethiourea as a
residue.

Information made available has indicated that the use of the
ethylenediamine analytical procedure was inefficient as an indicator
of residues of EBDCs and should be discarded. This would also mean the
withdrawal of the temporary tolerances for this compound recommended
by the 1974 Joint Meeting and the reversal of the decision to base
maximum residue limits on ethylenediamine content. Analytical methods
based on CS₂ evolution remain the only pragmatic procedures for the
general estimation of EBDC residues. The need for specific (or
group-specific) analytical methods remains unfulfilled.

The need to determine ETU arising from the use of
ethylenebisdithiocarbamates has been confirmed (see also monograph on
propineb); the temporary residue limits recommended in 1974 for ETU
are maintained as guideline levels. A recent collaborative study has
established a procedure for the determination of ETU residues in a
range of foods.

Very limited data were available concerning residues of the
dimethyldithiocarbamates ferbam and ziram or of thiram.

RECOMMENDATIONS

The temporary tolerances for ethylenediamine recommended by the 1974
Joint Meeting are withdrawn. The temporary maximum residue limits for
ETU are maintained as guideline levels, pending further information.

The importance of this group of fungicides is well recognized and
although it is not possible to recommend maximum residue limits for
the individual compounds (because of analytical considerations), It
would be helpful to set some general temporary maximum residue limits
to cover members of the dithiocarbamate fungicides as a group. From a
further study of data reported previously and some additional data
available to the meeting (including that on propineb), the following
limits appear to be adequate to cover the likely residues arising from
the use of single dithiocarbamate compounds on the crops listed. The
limits refer to residues, determined by CS₂ evolution and expressed
as CS₂, derived from ferbam, mancozeb, maneb, propineb, thiram,
zineb and ziram.

These limits are based on data arising from supervised trials in which
alkylenebisdithiocarbamates were used; coexisting residues of thiram
(or ferbam or ziram) from other treatments of the same crop could lead
to these levels being exceeded, especially on apples, lettuce,

tomatoes and strawberries. In such cases, separate analysis should be
made by the available method which is specific for thiram (AOAC,
1975).

Commodity Limits (as CS₂) mg/kg

Blackcurrants, celery,
grapes, red currants 5

Apples, peaches, pears,
strawberries, tomatoes 3

Bananas (whole), cherries,
endive, lettuce, melons,
plums 1

Beans (in pod), carrots,
cucumbers 0.5

Wheat 0.2

Bananas (pulp),
potatoes 0.1

FURTHER WORK OR INFORMATION

(a) Dithiocarbamates in general

REQUIRED (by July 1980)

1. A comprehensive survey of the use patterns of thiram, ferbam and
ziram.

2. Data on residues of thiram, ferbam and ziram from supervised
trials.

3. Data on residues of dithiocarbamates from crops grown under glass.

(b) Dimethyl dithiocarbamates

REQUIRED (by July 1980)

Further studies to investigate the haematological effects of thiram.

REQUIRED (by July 1980) (in addition to the toxicological information
listed in FAO/WHO 1975, P. 34)

1. Further data on the conversion of EBDC to ETU in various food
processing procedures.

2. Studies of procedures to minimize the formation of ETU during food
processing.

REFERENCES

Anonymous (1977) The ethylenediamine residue analytical method. Report
received from Rohm and Hass Co. (unpublished).

ACAC (1975) "Official methods of analysis", 12th Ed., 551-552.

Canada (1977) Data received from the Canadian Government
(unpublished).

FAO/WHO (1968) 1967 evaluations of some pesticide residues in food.
FAO/PL/1967/M/11/1; WHO/Food-Add./68:30.

FAO/WHO (1971) 1970 evaluations of some pesticide residues in foods
PAO/AGP/1970/X/12/1; WHO/Food Add./71.42. p. 269-283 and P.407 - 422

FAO/WHO (1975) 1974 evaluations of some pesticide residues in food.
FAO/AGP/1974¹/M/11; WHO Pesticide Residue Series, No. 4.

IUPAC (1977) Ethylenethiourea. Pure and Appl. Chem., 49:675-689.

Montedison Co. (1977) Residues of ethylenebisdithiocarbamates and
ethylenethiourea in grapes and wine (unpublished).

Netherlands (1977) Data received from the Netherlands Government
(unpublished).

Newsome, W.H. (1974) A method for determining
ethylenebis(dithiocarbamate) residues in food crops as
bis(trifluoroacentamido)ethane. J. Agr. Food Chem.p 22(5): 886-889.

Onley, J.H, Giuffrida, L., Ives, N.F., Watts, R.R. and Storherr,
R.W. (1977) Gas-liquid chromatography and liquid chromatography of
ethylenethiourea in fresh vegetable crops, fruits, milk and cooked
foods. J. Assoc. Off. Anal. Chem.# 60:1105-1110.

Onley, J.H. (1977) Gas-liquid chromatographic method for determining
ethylenethiourea in potatoes, spinach, apple sauce, and milk;
collaborative study. J. Assoc. Off. Anal, Chem., 60:1111-1115,

Otto, S., Keller, W., and Drescher, N. (1977) A new gas
chromatographic determination of ethylenethiourea residues without
derivatisation. J. Environ. Sci. Hlth., B 12(3):179-191.

Pease, H.L. and Holt, R.F. (1977) Manganese ethylenebisdithiocarbamate
(meneb)/ethylenothiourea (ETU) residue studies on five crops treated
with ethylenebisdithiocarbamate (EBDC) fungicides. J. Agric. Food
Chem., 25:561-567.

Phillips, W.F., Grady, M.D. and Freudenthal, R. (1977) Effects of food
processing on residues of two ethylenebisdithiocarbamate (EBDC)
fungicides and ethylenethiourea (ETU). Environmental Health Effects
Research Series, EPA-600/1-77-021, EPA, North Carolina, USA.

Winell, B. (1975) Ditiokarbamatrester i frukt bär, grönsaker och
potatis. Vär föda No. 2, 1-9.

    See Also:
       Toxicological Abbreviations
       Dithiocarbamate Fungicides (AGP:1970/M/12/1)