Organophosphorus and Carbamate Insecticides - Organic Pollutants: An Ecotoxicological Perspective - page 207

taBLe 10.2
toxicity of organophosphorus Insecticides

type of measurement
(units) compound Species Value

Parathion Rat Acute oral LD 50 (mg/kg) 3-6

Malathion Rat Acute oral LD 50 (mg/kg) 480-5600

Dimethoate Rat Acute oral LD 50 (mg/kg) 150-300

Dimethoate Birds (4) Acute oral LD 50 (mg/kg) (26)

Diazinon Rat Acute oral LD 50 (mg/kg) 235-1250

Diazinon Birds (4) Acute oral LD 50 (mg/kg) (4.5)

Diazinon Fish 96 h LC 50 (mg/L) 0.09-2.76

Demeton- S -methyl Rat Acute oral LD 50 (mg/kg) 35-129

Demeton- S -methyl Birds Acute oral LD 50 (mg/kg) 10-50

Demeton- S -methyl Fish 96 h LC 50 (mg/L) 0.6-60

Disyston Rat Acute oral LD 50 (mg/kg) 12.5

taBLe 10.3
Properties of Some carbamate Insecticides

water Solubility
(µg/mL @ 25°c)

Vapor Pressure
(mm Hg @ 25°c)

compound log K ow

Carbaryl 40 2.36 3 × 10 −3

Propoxur 1000 3 × 10 −5 (30°C)

Aldicarb 6000 1.36 1 × 10 −4

Carbofuran 700 1 × 10 −5

Some OPs listed in Table 10.3 that are of exceptionally high toxicity (e.g., para-
thion) are no longer used in Western countries because they are considered too haz-
ardous. In Table 10.2, the toxicity of diazinon and dimethoate to birds is given as a
mean value for four different species. This is to emphasize the relatively high avian
toxicity of these compounds in birds in comparison with rats and other mammals
(see Environmental Health Criteria 198). The reason for this selectivity is discussed
in Section 10.2.2. Similar selectivity is shown by the OPs pirimiphos-methyl and
pirimiphos-ethyl, which are related structurally to diazinon. These compounds can
present a serious hazard to birds when used in agriculture. Disyston (disulfoton)
and the related compound phorate (thimet) are highly toxic to vertebrates generally
and are normally formulated as granules, which only slowly release the insecticide.
Granules limit the availability of the insecticide, and are therefore safer to use and
present less risk to the environment than more readily available formulations such as
emulsifiable concentrates. OPs are often very toxic to fish (see, for example, the data
for demeton- S -methyl and diazinon) and aquatic invertebrates. In the case of the lat-
ter, toxic effects have been reported following exposure to levels as low as 0.01 mg/L
in ambient water (Environmental Health Criteria 63).