Tebuthiuron in freshwater and marine water

Toxicant default guideline values for protecting aquatic ecosystems

October 2000

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

Tebuthiuron (CAS 34014-18-1) is a non-selective, systemic, urea soil-herbicide, introduced by Eli Lilly & Co (now DowElanco). Its IUPAC name is 1-(5-tert-butyl-1,3,4-thiadiazol-2-yl)-1,3-dimethylurea, formula C₉H₁₆N₄OS and molecular weight 228.3. It is soluble in water to 2.5 g/L at 25°C and has a low log K_ow of 1.8 (Tomlin 1994). The current analytical practical quantitation limit (PQL) for tebuthiuron in water is 1 µg/L (NSW EPA 2000).

Uses and environmental fate

Tebuthiuron is used for total control of herbaceous and woody plants in areas not used for cropping, e.g. pastures, industrial areas. (Tomlin 1994). It is adsorbed by roots and readily translocated and tends to persist in soils (Tomlin 1994). Hence it can potentially damage desirable trees and shrubs if used off target. Its breakdown is slower in dry soils or in presence of high organic context.

Aquatic toxicology

Freshwater fish: three species, 96-hour LC50, 106,000 to 291,000 µg/L; chronic, Pimephales promelas, 33-day NOEC (growth), 9300 µg/L and 7-day NOEC (mortality), 90,000 µg/L. Oncorhynchus mykiss 45-day NOEC (mortality) 26,000 µg/L.

Freshwater amphibian: Rana catesbelana, 72-hour LC50, 316,000 µg/L.

D. magna, 48-hour EC50, 297,000; chronic 21-day NOEC (reproduction), 21,800 µg/L.

Freshwater hydra: H. viridissima, 96-hour NOEC (growth) 50,000 µg/L.

Freshwater algae: Selenastrum capricornutum, 96-hour LC50, 80 to 102 µg/L; chronic 5 to 6-day NOEC (growth and population growth), 10 to 50 µg/L; diatom, Navicula pelliculosa, 7-day NOEC growth, 56 µg/L; B-G alga Anabaena flosaquae, 7-day NOEC, 310 µg/L.

Freshwater mesocosms: most mesocosm studies with tebuthiurion have focused on aquatic plants, due to its high toxicity to these. Temple et al. (1991) also included fish and invertebrates in pool mesocosms in exposures of 10 to 1000 µg/L. They found algal primary productivity and chironomid biomass were affected at ≥200 µg/L but no effects were detected at lower concentrations. A NOEC value of 52 µg/L was reported for net primary productivity of periphyton.

These did not meet the minimum data requirements but indicate that the trigger value is likely to be sufficiently protective.

Marine crustacean: one species, 96-hour LC50, 48,000 µg/L.

Marine diatom: one species, Skeletonema costatum,7-day NOEC, 38 µg/L.

Australian and New Zealand data

The Hydra sp. data were from Australia.

Guidelines

The freshwater data for tebuthiuron was distinctly bimodal and there were insufficient data in each mode to use the statistical distribution method.

A freshwater high reliability trigger value of 2.2 µg/L was derived for tebuthiuron using the statistical distribution method with 95% protection. In the absence of marine data, the freshwater figure of 2.2 µg/L was adopted as a marine low reliability trigger value. This figure should only be used as an indicative interim working level.

References

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.

NSW EPA 2000. Analytical Chemistry Section, Table of Trigger Values 20 March 2000, LD33/11, Lidcombe, NSW.

Temple AJ, Murphy BR & Chesak EF 1991. Effects of tebuthiuron on aquatic productivity. Hydrobiologia, 224, 117-127.

Tomlin C 1994. The pesticide manual: A world compendium. 10th edn, British Crop Protection Council & Royal Society of Chemistry, Bath, UK.