Agriculture Reference
In-Depth Information
expressed as violent seizu res. Convu lsions caused by the more slowl y
metab olized cyclodienes may recur over periods of several days. Convulsions
may cau se death by int erfering wit h pul monary gas exchange and by gen-
era ting severe metabolic acidosis. Various disturbances of sensation, coordi-
nation, and mental function are also characteristic of acute organochlorine poi-
soning. High tissue concentrations of organochlorines increase myocardial
irritability, predisposing to cardiac arrhythmias. When tissue organochlorine
con centr ation s dro p bel ow thr eshol d lev els, rec overy fro m the poi sonin g
occurs. Organochlorines are not cholinesterase inhibitors.
High tissue levels of some organochlorines (notably DDT, DDE, cyclodi-
enes, mirex, and kepone) have been shown to induce hepatic microsomal
drug-metabolizing enzymes. This tends to accelerate excretion of the pesti-
cides themselves, but may also stimulate biotransformation of critical natural
substances, such as steroid hormones and therapeutic drugs, occasionally ne-
cessitating reevaluation of required dosages in persons intensively exposed to
organochlorines. Human absorption of organochlorine sufficient to cause en-
zyme induction is likely to occur only as a result of prolonged intensive expo-
sure.
Hexachlorobenzene (a fungicide) has caused porphyria cutanea tarda in
humans. It does not cause convulsions. Lindane, chlordane, and dieldrin have
been associated anecdotally with certain rare hematologic disorders, including
aplastic anemia; the incidence of these effects appears to be extremely low.
Poisoning by endosulfan has caused blindness in sheep. Mirex at high
dosage produces cataracts in rats and mice. The DDT analogue known as
DDD is selectively concentrated in adrenal tissue, where high levels have an
inhibitory effect on corticosteroid synthesis, and a damaging effect on the
cells. Certain other organochlorines are also bioconcentrated in the adrenal
cortex.
d.
Insecticides of Biological Origin
This section will cover several widely used insecticidal products of natural
origin, and also a growth promoting agent, gibberellic acid. It discusses, in
order, pyrethrum and pyrethrins, nicotine, rotenone, sabadilla, bacillus thur-
ingiensis, and gibberellic acid.
1.
Pyrethrum and Pyrethrins
Pyrethrum is an extract of dried chrysanthemum flowers. The extract con-
tains about 50% active insecticidal ingredients known as pyrethrins. The ke-
toalcoholic esters of chrysanthemic and pyrethroic acids are known as pyre-
thrins, cinerins, and jasmolins. These strongly lipophilic esters rapidly pene-
trate many insects and paralyze their nervous systems. Both crude pyrethrum
