These two cases illustrate the conversion of insecticides to products that are more 
toxic to insects and are considered, by some, to be more toxic to man, The fate of the 
epoxides is not known, but it has been shown that they are more stable than the original 
materials. Recent studies also have indicated the presence of compounds other than 
heptachlor and heptachlor epoxide in plants after technical heptachlor has been applied, 
Investigations are now being made to identify these compounds. 
The mechanism of the conversion to epoxides is not known, but it is thought that in 
soils microorganisms may be at least partly responsible, In animals the conversion 
appears to be practically complete, and takes place rapidly. Only traces of aldrin and 
heptachlor have been found in animal tissues following feeding of these compounds 
whereas relatively large amounts of their epoxides are formed and stored, 
ORGANIC-PHOSPHORUS COMPOUNDS 
The first ofthe organic-phosphorus insecticides to gain widespread use was parathion. 
This compound is converted to the S-ethyl isomer by heating. A more toxic compound, 
para-oxon, is formed by enzymatic action in plants, as follows: 
In animals the additional products p-nitrophenol and p-aminophenol are also formed 
(11). Not much seems to be known regarding the decomposition products of parathionin 
soils, 
Phorate, another organic-phosphorus insecticide coming into widespread use, is 
rapidly metabolized in plants to sulfoxide and sulfone forms. Bowman and Casida (2) 
have found the metabolic pathway, in cotton, to be as follows: 
Ss S) O Ss O 
C.H-O | CaHeOn || ll Gt I 
eo S P-S-CHy-S- C,H, —> oe > P-S-CH,-S-CH, —> Zo ~P-S-CH,-S-CoH, 
CHO C5H.0 CH.0 
O 
Phorate Phosphorodithioate Phosphorodithioate 
Sulfoxide Sulfone 
O O O O 
aee@le || | CAHeOmnt I 
2° DP-S-CHy-S-CoH, Z2 P-S- CH-S~CH, 
Care@ CAH=O {| 
PD) 25 0 
Phosphorothiolate Phosphorothiolate 
Sulfoxide Sulfone 
In this instance phorate, a weak cholinesterase inhibitor, is converted into a very 
potent inhibitor, the phosphorothiolate sulfone. Phorate is very effective in plants grown 
108 
