untreated samples. Over 10% of the soil and earthworm 
samples were checked by thin-layer chromatography; the 
results were very similar to those from the gas chromato- 
graphic analysis. It is therefore unlikely that there was any 
significant interference from PCB's, either initially or dur- 
ing the study. 
Recovery Values 
Soil and earthworm samples from a field where pesti- 
cides had not been applied were each homogenized and 
subsampled for analysis. Two subsamples of each were 
analyzed for organochlorine insecticides. The remaining 
subsamples were fortified with analytical grade com- 
pounds to determine recovery percentages (Table 1). Per- 
cent recoveries were corrected for amounts in the un- 
treated samples, but the residue data were not adjusted for 
the percent recoveries. 
Residue Values 
Insecticides detected in soils and earthworms are ex- 
pressed on a parts-per-million, dry weight basis. Because 
moisture is lost in earthworms held in freezers for extended 
periods of time (Davis 1966), dry weight seemed to be a 
more precise method for comparing residues in earth- 
worms with residues in soils. 
The limits at which insecticide values could be depend- 
ably quantified varied with the sample size. Soil samples 
usually were of uniform size, and the limits of quantifica- 
tion were either 0.005 or 0.006 ppm, dry weight. At times 
earthworms were difficult to obtain and quantities varied 
accordingly. The limits of quantification also varied and 
were either 0.012, 0.017, or 0.020 ppm, wet weight. Resi- 
dues detected below these limits are expressed as trace 
amounts, 
Statistical Methods 
The variances of the residues were proportional to their 
arithmetic means. Wheatley and Hardman (1968) made 
similar observations concerning residues in soils and earth- 
worms, Gish (1970) confirmed these observations, point- 
ing out that residues in soils and earthworms were posi- 
tively skewed and that logarithmically transformed data 
presented a more nearly normal frequency distribution. 
All residue data were transformed to common logarithms 
before statistical techniques were applied. Trace values 
were quantified for statistical treatment by dividing the 
values for the limits of detection by 2 and expressing each 
quotient on a dry weight basis. The level of significance 
for differences between values was accepted as P < 0.05 
unless otherwise indicated. Duncan’s multiple range test 
(Duncan 1955) was used to test for significance in Tables 
3, 5, and 6. 
Residue Concentration and Change 
Dieldrin Plots 
Two subsamples of the wettable powder formulation of 
“50%” technical dieldrin averaged 44.6% active ingredi- 
ents. These include 43.1% dieldrin, 1.2% endrin, and 
0.3% aldrin. 
Dieldrin was the principal residue found in the dieldrin 
plots, occurring in all samples. Quantities of dieldrin 
accounted for more than 95% of all organochlorine insect- 
icides in the soil and 93% in the earthworms. Aldrin was 
detected in 26 of 72 soil samples and in 5 of 72 earthworm 
samples in amounts at or near the limits of detection. 
Endrin occurred in 11 of 72 soil samples in amounts that 
did not exceed 0.2 ppm and in 2 of 72 earthworm samples 
in amounts that did not exceed 1.0 ppm. The other 
Table 1. Average percentages of insecticides recovered when known amounts were added to soils and earthworms.* 

Concentrations (ppm wet weight) of compound added to soils and earthworms 




Soils Earthworms 
Compound 
added 0.05 5.0 0.5 5.0 50.0 500.0 
Dieldrin 70.0 79.8 77.8 — 79.4 ~ 
p,p'-DDE 109.0 107.5 96.5 — 95.1 - 
p,p'-DDD 124.0 117.5 93.5 _ 97.2 — 
p.p'-DDT 101.0 104,2 88.3 — 91.0 — 
o,p'-DDT 107.5 111.6 95.0 — 92.5 = 
Heptachlor 72.0 91.8 72.5 46.0(2) 94.0 31,8(2) 
Heptachlor epoxide 81.0 92.1 79.5 92.0(2) 93.5 68.0(2) 
a-chlordane 86.0(2) 90.6(2) 62.0(2) 91.0(2) 60.6(2) 71.2(2) 
+-chlordane 84.0(2) 91.4(2) 58.0(2) 98.0(2) 57,5(2) 73.8(2) 

aBach value represents the arithmetic mean of four subsamples, except where indicated by numbers in parentheses. Recovery values 
were corrected for background levels in soils and earthworms. 

