


100 Aa 
| fer \ / 
- Cy Lees ra 
© if VA / > 
° A ee 
> b ow” \\ a ae. ‘NZ oe 
malo wv (oboe / are ra 
é AY Sa 
L o— — A 
: ~ N 7 
Zz 
el 
A 
A 4 B 12 16 20 24 
TIME SINCE APPLICATION, MONTHS 
Fig. 1. Mean quantities of dieldrin in soils (solid lines) and earth- 
worms (broken lines) at various times following a single appli- 
cation of 50% wettable powder dieldrin at 0.56 (circles), 2.24 
(squares), or 8.97 (triangles) kg ai/ha. 
organochlorine insecticides detected in these plots 
included, in decreasing order of abundance, DDE, DDD, 
p,p'-DDT, heptachlor epoxide, and y-chlordane. 
Each line depicting dieldrin levels in soils and earth- 
worms in Fig. 1 represents the arithmetic mean of two 
replicates (plots); the replicates were not significantly dif- 
ferent. Dieldrin in soils and earthworms differed among 
treatment levels (P < 0.01). The relation of dieldrin in 
soils to the amount applied was parabolic, dieldrin resi- 
dues increasing at an accelerating rate with increasing 
levels of application. Dieldrin in earthworms increased 
linearly (P < 0,01) with increasing rates of application. 
No discernible loss of dieldrin was detected from soils 
after 2 years. Infrequently, dieldrin levels differed among 
sampling periods (P < 0.01); however, levels among most 
periods were not statistically different (Table 2). No dis- 
tinct trend of increase or loss was evident from the fluctua- 
tions of soil residues with time (Table 2) or as tested by 
simple linear regressions. 
A slight decline of dieldrin in earthworms occurred ini- 
tially, but then dieldrin increased until a maximum was 
reached in September, 4 months after application (Table 
3). At 4 months, earthworms from plots treated at 0.56, 
2.24, and 8.97 kg ai/ha averaged 11, 71, and 162 ppm of 
dieldrin. From a maximum in early fall, there was a sharp 
decline to a depression in winter through early spring. A 
subsequent increase to another, less prominent, elevation 
took place from late spring through early fall, a decrease 
again in winter, and another increase in late spring. Sea- 
sonal fluctuations generally were statistically significant, 
but subsequent elevations were always less than the maxi- 
mum at 4 months, Underlying the seasonal fluctuations 
was a general decline of dieldrin in earthworms during the 
2-year study, This decline, illustrated by simple linear 
regression equations (Table 4), was significant (P < 0.01) 
only for earthworms from the 0,56 and 2.24 kg ai/ha 
plots. 
Dieldrin in earthworms was not significantly correlated 
with dieldrin in soils over the 2-year period. The low cor- 
relation probably was due to the dieldrin fluctuating sea- 
sonally in earthworms but not in soils, Correlations were 
much greater for samples collected within one season, and 
most were significant. 
The ratios of dieldrin in earthworms to dieldrin in soils 
were also examined. The ratios were calculated by divid- 
ing the ppm, dry weight, in earthworms by the ppm, dry 
weight, in soils, and were called storage-exposure ratios 
(Table 5). No statistical differences occurred between 
replications or among dosage levels, but there were dif- 
ferences (P < 0.01) among sampling periods, Residues in 
earthworms averaged 166 times those in soils in the sam- 
pling period 4 months after application, when earthworm 
residues reached a maximum. Fluctuations in these ratios 
followed the cyclic pattern of dieldrin in earthworms; ele- 
vations lasted from late spring to early fall and troughs 
lasted from winter to early spring. Even during a trough, 
dieldrin residues in earthworms averaged at least 5.3 times 
those in soils. 
Other variables in this study (Table 6) were examined 
for their influence on dieldrin concentrations in soils and 
earthworms by using a stepwise procedure (Draper and 
Smith 1968) for multiple linear regression. The combined 
influence of percent organic matter and percent soil mois- 
ture, although significant (P < 0.01), accounted for only 
19.4% of the variability in soil levels of dieldrin. Soil pH, 
months after treatment, and rainfall during the 2 weeks 
before sampling did not significantly affect soil levels. 
About 77.2% (P < 0.01) of the variability in earthworm 
residues was accounted for by the regression equation 
A 
Y = —3.70553 + 0.52248 X, — 0.03787 X, + 0.06699 X, 
+ 0.09025 X, + 0.25352 X. 
where Y is the predicted logarithm of ppm dieldrin in 
earthworms, X, is the logarithm of ppm in soils, Xq is 
months after treatment, Xj is the percentage moisture in 
earthworms, X, is inches of rainfall during the 2 weeks 
before sampling, and X; is the percent lipid in earth- 
worms, This equation describes the relation of dieldrin in 
earthworms to other measured variables, and may prove 
useful for predicting quantities of dieldrin in earthworms 
for some period of years after application. 
Dieldrin residues in soils and earthworms were meas- 
ured in Missouri for 2% and 5 years (Korschgen 1970, 
1971). (Statements of significance concerning these studies 
