Demeton-S in freshwater and marine water

Extracted from Section 8.3.7 ‘Detailed descriptions of chemicals' of the ANZECC & ARMCANZ (2000) guidelines.

The default guideline values (previously known as ‘trigger values’) and associated information in this technical brief should be used in accordance with the detailed guidance provided in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality.

Description of chemical

Organophosphorus pesticides are derivatives of phosphoric, phosphonic, phosphorothioic, or phosphonothioic acids, comprising many chemicals with a wide range of uses (WHO 1986). They exert their acute effects in insects, fish, birds and mammals by inhibiting the acetylcholinesterase (AChE) enzyme, but may also have a direct toxic effect (WHO 1986).

Demeton-S (CAS 8065-48-3) is a phosphorothioate OP pesticide, first introduced by Bayer AG, as one component of a mixture with demeton (CAS 298-03-3). Its IUPAC name is O,O-diethyl-O-2-ethylthioethyl phosphorothioate, formula is C8H19O3PS2 and molecular weight of 258.

Uses and environmental fate

Demeton-S is not currently in use. See Demeton-S-methyl for details of environmental fate.

Aquatic toxicology

Demeton had high-moderate toxicity to a small range of species.

Freshwater fish: four species, 96-hour LC50, 40 to 130 for Lepomis macrochirus; 150 to 530 µg/L forOncorhynchus mykiss and 3600 to 16,000 for Ictalurus punctatus andPimephales promelas.

Marine fish: one species, Leistomus xanthurus, 48-hour LC50, 320 to 550 µg/L.

Marine molluscs: one species, 96-hour EC50 (growth), 2000 µg/L.

Australian and New Zealand data

Unpublished Australian data range from 0.01 to 0.08 mg/L for Ceriodaphnia dubia (Warne pers. comm. 2000). These data were not used for calculations.

Factors causing variations in toxicity

The low water solubility and high log Kow indicate that deltamethrin would be strongly bound to sediment or suspended matter and would be transient in the water column.


There were insufficient data to derive reliable guideline figures for demeton-S. Indicative interim working levels (low reliability trigger values) of 0.04 µg/L for freshwater and 0.3 µg/L for marine waters were derived using an assessment factor (AF) of 1000.


ANZECC & ARMCANZ 2000. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra.

WHO 1986. Environmental health criteria 63. Organophosphorus insecticides: A general introduction. World Health Organization, Geneva.