Persistence of Carbofuran Residues in Some British Columbia Soils by I. H. WILLIAMS,M. J. BROWN Research Station, Agriculture Canada, Vancouver, B.C. V6T 1X2 and P. WHITEHEAD
Canadian ~FildliJe Service, Environment Canada, Vancouver, B. C.
Carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) has been used in British Columbia since 1970 for the control of a number of soil insects such as w i r e w o r m s and root maggots. A l t h o u g h a number of studies have been r e p o r t e d on the d e g r a d a t i o n of this insecticide (GETZIN 1973; CARO et al. 1973; READ 1969) d e t a i l e d knowledge of its behavior under local conditions has been lacking. As a preliminary to a more complete study, soils which had been treated w i t h carbofuran one and/or two years p r e v i o u s l y were sampled and analysed. S u r p r i s i n g l y high residues were found and there was evidence of build-up where treatments were repeated for two successive years.
EXPERIMENTAL In M a r c h 1975 soil samples were taken from two areas in the Fraser Valley. Three fields were tested; two were subdivided, one into three and the other into four areas according to c a r b o f u r a n use. Each subdivision was sampled separately. The samples, consisting of twenty 1 5 x 2.5 cm cores, were thoroughly mixed then held in frozen storage until analysed. Analysis: 20 g samples of soil were extracted by shaking for three 2 hr periods w i t h 70 ml portions of a 2:5 v/v m e t h a n o l : d i c h l o r o m e t h a n e mixture. The combined extracts w e r e c o n c e n t r a t e d until free of methanol then p a r t i t i o n e d into dichloromethane. C l e a n - u p on alumina and glc d e t e r m i n a t i o n with a C o u l s o n c o n d u c t i v i t y detector in the nitrogen m o d e w e r e as p r e v i o u s l y described (WILLIAMS and BROWN 1973). Results were corrected for soil m o i s t u r e content.
242 Bulletin o f Environmental Contamination & Toxicology,
Vol. 15, No. 2 @ 1976 by Springer-Verlag New York Inc.
P~SULTS Table I shows sampled.
AND D I S C U S S I O N
the r e s i d u e s
found
TABLE Carbofuran Soil
I
Residues
After
type
in the eight
areas
I One and Two Year
Year(s) of treatment
Periods
C a r b o f u r a n found ppm (dry weight)
Poorly drained Clay-muck
1 2 3* 4
Control 1973 & 1974 1973 1973
0.17 2.62 0.78 1.18
Well d r a i n e d Clay-muck
1 2 3
1974 1973 1973
2.08 3.88 0.73
1
1974
I~ P o o r l y Clay
drained
& 1974
0.38
* area of b e t t e r
drainage
The data are i n s u f f i c i e n t to d r a w firm c o n c l u s i o n s but the f o l l o w i n g o b s e r v a t i o n s are relevant. The c a r b o f u r a n levels are r e m a r k a b l y high. The r e c o m m e n d e d a p p l i c a t i o n rate of 50 ib/acre F u r a d a n 10G (5 Ib a.i.) should r e s u l t in an initial c o n c e n t r a t i o n of 2.5 ppm b a s e d on a 6 in. acre of 2 x 10Glb. Thus d e g r a d a t i o n a p p e a r s to have been p a r t i c u l a r l y slow in these soils. Moreover, a b u i l d - u p of c a r b o f u r a n is a p p a r e n t in fields t r e a t e d for two s u c c e s s i v e years. This w o u l d indicate a need for the study to be c o n t i n u e d in o r d e r to s u b s t a n t i a t e these r e s u l t s and to d e t e r m i n e the d e g r e e of r e s i d u e b u i l d - u p and rate of d e g r a d a t i o n over a p e r i o d of s e v e r a l years of treatment.
REFERENCES CARO,
J.H., FREEM~N, H.P., G L O T F E L T Y , and EDWARDS, W.M.: J. Agr. i010 (1973).
GETZIN, READ,
L.W.:
D.C.:
WILLIAMS,
Environ. J. Econ.
Entomol.
Entomol.
I.H., and BROWN, 21, 399 (1973).
62,
M.J.:
243
[,
D.E., TURNER, B.C., Food Chem. 21,
461
(1973).
1338
(1969).
J. Agr.
Food
Chem.
Canadian ~FildliJe Service, Environment Canada, Vancouver, B. C.
Carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) has been used in British Columbia since 1970 for the control of a number of soil insects such as w i r e w o r m s and root maggots. A l t h o u g h a number of studies have been r e p o r t e d on the d e g r a d a t i o n of this insecticide (GETZIN 1973; CARO et al. 1973; READ 1969) d e t a i l e d knowledge of its behavior under local conditions has been lacking. As a preliminary to a more complete study, soils which had been treated w i t h carbofuran one and/or two years p r e v i o u s l y were sampled and analysed. S u r p r i s i n g l y high residues were found and there was evidence of build-up where treatments were repeated for two successive years.
EXPERIMENTAL In M a r c h 1975 soil samples were taken from two areas in the Fraser Valley. Three fields were tested; two were subdivided, one into three and the other into four areas according to c a r b o f u r a n use. Each subdivision was sampled separately. The samples, consisting of twenty 1 5 x 2.5 cm cores, were thoroughly mixed then held in frozen storage until analysed. Analysis: 20 g samples of soil were extracted by shaking for three 2 hr periods w i t h 70 ml portions of a 2:5 v/v m e t h a n o l : d i c h l o r o m e t h a n e mixture. The combined extracts w e r e c o n c e n t r a t e d until free of methanol then p a r t i t i o n e d into dichloromethane. C l e a n - u p on alumina and glc d e t e r m i n a t i o n with a C o u l s o n c o n d u c t i v i t y detector in the nitrogen m o d e w e r e as p r e v i o u s l y described (WILLIAMS and BROWN 1973). Results were corrected for soil m o i s t u r e content.
242 Bulletin o f Environmental Contamination & Toxicology,
Vol. 15, No. 2 @ 1976 by Springer-Verlag New York Inc.
P~SULTS Table I shows sampled.
AND D I S C U S S I O N
the r e s i d u e s
found
TABLE Carbofuran Soil
I
Residues
After
type
in the eight
areas
I One and Two Year
Year(s) of treatment
Periods
C a r b o f u r a n found ppm (dry weight)
Poorly drained Clay-muck
1 2 3* 4
Control 1973 & 1974 1973 1973
0.17 2.62 0.78 1.18
Well d r a i n e d Clay-muck
1 2 3
1974 1973 1973
2.08 3.88 0.73
1
1974
I~ P o o r l y Clay
drained
& 1974
0.38
* area of b e t t e r
drainage
The data are i n s u f f i c i e n t to d r a w firm c o n c l u s i o n s but the f o l l o w i n g o b s e r v a t i o n s are relevant. The c a r b o f u r a n levels are r e m a r k a b l y high. The r e c o m m e n d e d a p p l i c a t i o n rate of 50 ib/acre F u r a d a n 10G (5 Ib a.i.) should r e s u l t in an initial c o n c e n t r a t i o n of 2.5 ppm b a s e d on a 6 in. acre of 2 x 10Glb. Thus d e g r a d a t i o n a p p e a r s to have been p a r t i c u l a r l y slow in these soils. Moreover, a b u i l d - u p of c a r b o f u r a n is a p p a r e n t in fields t r e a t e d for two s u c c e s s i v e years. This w o u l d indicate a need for the study to be c o n t i n u e d in o r d e r to s u b s t a n t i a t e these r e s u l t s and to d e t e r m i n e the d e g r e e of r e s i d u e b u i l d - u p and rate of d e g r a d a t i o n over a p e r i o d of s e v e r a l years of treatment.
REFERENCES CARO,
J.H., FREEM~N, H.P., G L O T F E L T Y , and EDWARDS, W.M.: J. Agr. i010 (1973).
GETZIN, READ,
L.W.:
D.C.:
WILLIAMS,
Environ. J. Econ.
Entomol.
Entomol.
I.H., and BROWN, 21, 399 (1973).
62,
M.J.:
243
[,
D.E., TURNER, B.C., Food Chem. 21,
461
(1973).
1338
(1969).
J. Agr.
Food
Chem.
