DDT 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
Most organochlorine pesticides have been phased out of use in recent years, mainly because of their residual properties and potential for bioaccumulation. The guideline trigger values stated are for toxicity only and need to be adjusted for bioaccumulation where appropriate. Where the statistical distribution method was used, figures quoted are the 95% protection levels, usually applicable to slightly to moderately disturbed systems although 99% protection figures are recommended for chemicals that bioaccumulate.
DDT (CAS 50-29-3) is a persistent organochlorine insecticide which has gained notoriety for its worldwide distribution, bioaccumulation and effects on birds of prey (Matsumura 1985). DDT has been banned from general use in the USA since 1972 and in Australia since 1987 (ANZEC 1991) but its use in parts of Asia has been increasing (Iwata et al. 1994). DDT is a global pollutant and its continued use in tropical countries can lead to low-level contamination in remote areas through long-range transport (Iwata et al. 1993).
Its chemical name is 1,1'-bis(p-chlorophenyl)-2,2,2-trichloroethane, formula is C14HCl5 and molecular weight is 354.5. It has very low water solubility (3.10 to 0.34 µg/L at 25°C) and a high log Kow of 6.36. The current analytical practical quantitation limit (PQL) for DDT is 0.05 µg/L (NSW EPA 2000).
Uses and environmental fate
DDT was commonly used in the 1970s as an insecticide for cotton and tobacco and is still in use in Asia, Africa and Central America for control of vectors for malaria, yellow fever and sleeping sickness (HSDB 1996). DDT adsorbs strongly to soil (Koc 1.13 x 105) and both suspended and bottom sediments, and it only biodegrades appreciably under anaerobic conditions. Photodegradation occurs very slowly in air and water. The half-life of evaporation from water is up to 50 hours. Bioconcentration factors vary for fish from 600 to 100 000, for snails from 3660 to 34,500, for mussels from 4550 to 690,000, for oysters from 700 to 70,000 (Reish et al. 1978, HSDB 1996). Some figures range up to 106 (HSDB 1996). Some of these figures were obtained from exposures as low as 80 ng/L (Johnson & Finley 1980).
Accumulation of DDT residues was significantly less in mosquitofish in 15 g/L saline water than in freshwaters (Murty 1986). Sediments can be a continuing source for contamination of aquatic life (Green et al. 1986). Major degradation products of DDT include DDD (also previously used as an insecticide) and DDE. The p,p'-isomer is more toxic to invertebrates than the o,p-isomer. Temperature and hardness did not significantly affect toxicity of DDT, with only a slight increase in toxicity to P. promelas between 7 and 29°C (Johnson & Finley 1980).
DDT has very high toxicity to most species, except for moderate to low toxicity to freshwater molluscs, algae and flatworms.
Freshwater fish: 30 spp, 96 hours (48 hours only for 1 species), 0.45 to 123 µg/L. Some outlying figures were above the water solubility; Cyprinus carpio (350 and 540 µg/L) and additional insensitive species Cirrhinus mrigala (6400 µg/L), Heteropneustes fossilis (2950 µg/L), Macropodus cupanus (2277 µg/L). Chronic NOEC figures were reported for Gambusia holbrooki (45-day mortality, 0.55 µg/L; 30-day and 45-day reproduction, 0.55 and 0.14 µg/L) and Pimephales promelas (266-day mortality, 0.35 µg/L).
Freshwater amphibian: 1 sp, 96-hour LC50, 30 µg/L, above the water solubility.
Freshwater crustaceans: 12 spp, 48 to 96-hour LC50, 0.36 to 6.10 µg/L. Additional outlying species were an ostracod Cypridopsis vidua (48 hours, 15 to 54 µg/L), a crab Paratelphusa cunicularis (96 hours, 560 µg/L) and anomalous result for D. obtysa of 8700 µg/L (48 hours). Chronic NOEC figures of 0.050 to 0.067 µg/L (reproduction and mortality) were reported for D. magna.
Freshwater insects: 12 spp, 48 to 96-hour LC50, 1 to 23 µg/L. Two additional species showed extreme variations in results, which could not be checked: mosquito Aedes aegypti (1 to 1261 µg/L) and a stonefly Pteronarcys californica (7 to 3800 µg/L).
Freshwater molluscs: 1 sp, 96-hour LC50, 17,000 µg/L, well above the water solubility.
Freshwater Platyhelminthes: 1 sp, 96-hour LC50, 1050-1100 µg/L, above the water solubility.
Freshwater algae and ciliates: 2 spp, 72 to 96 hour LC50, 4600 to 15,000 µg/L, above the water solubility.
Marine fish: 10 spp, 48 to 96-hour LC50, 0.26 to 10 µg/L.
Marine crustaceans: 10 spp, 48 to 96-hour LC50, 0.45 to 120 µg/L. Copepods, mysids and Penaeus duorarum were among the most sensitive (≤ 2.5 µg/L) and, interestingly, other related shrimps were least sensitive (28 to 120 µg/L, above the solubility). A chronic NOEC (14-day reproduction) for Nitocra spinipes (copepod) of 0.1 µg/L gave an acute-to-chronic ratio (ACR) of 25.
Marine molluscs: 4 spp, 96-hour LC50, 9.4 to 14.2 µg/L, above the water solubility.
Marine algae: only 24-hour NOEC (growth) figures were available for two diatoms, both 1 µg/L.
Factors that affect toxicity
Dust and wettable powder formulations of DDT had much lower toxicity than liquid formulations, by a factor of 10 to 20, but this may not reduce bioaccumulation potential. DDT was much less toxic to Oryzias latipes (10,000 µg/L) at 10°C than at 20°C or 30°C (280 to 400 µg/L).
Australian and New Zealand data
Toxicity of DDT formulation to the introduced mosquitofish, Gambusia holbrooki, varied from 2.8 to 14.6 µg/L (96-hour LC50). The firetail gudgeon, Hypseleotris gallii, was less sensitive, with a 96-hour LC50 of 34.1 µg/L but still within the range for overseas species. The 45-day chronic NOEC (reproduction) for G. holbrooki was 0.14 µg/L.
A freshwater moderate reliability guideline figure of 0.01 µg/L was derived for DDT using the statistical distribution method with 95% protection and an ACR of 71 (geometric mean of all). The 99% protection level was 0.006 µg/L and is recommended as the trigger value for slightly-moderately disturbed systems.
A marine low reliability trigger value of 0.0004 µg/L was calculated for DDT using an initial AF of 10 and an ACR of 71 on the lowest acute fish figure. This figure should only be used as an indicative interim working level.
Both of these need to be adjusted for bioaccumulation. Users are advised to apply the 99% protection level if there are no data to adjust for bioaccumulation at the specific slightly-moderately disturbed site (Section 188.8.131.52 of the ANZECC & ARMCANZ 2000 guidelines).
ANZEC 1991. Persistent organochlorine compounds in the marine environment. Australian and New Zealand Environment Council, Australian Government Publishing Service, Canberra.
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.
Green DR, Stull JK & Heesen TC 1986. Determination of chlorinated hydrocarbons in coastal waters using a moored in situ sampler and transplanted live mussels. Marine Pollution Bulletin 17, 324-329.
HSDB (Hazardous Substances Data Bank) 1996. Micromedex Inc. 31 July 1996.
Iwata H, Tanabe S, Sakai N & Tatsukawa R 1993. Distribution of persistent organochlorines in the oceanic air and surface seawater and the role of ocean on their global transport and fate. Environmental Science and Technology 27, 1080-1098.
Johnson WW & Finley MT 1980. Handbook of acute toxicity of chemicals to fish and aquatic invertebrates. US Department of the Interior, Fish and Wildlife Service, No 137, Washington DC.
Matsumura F 1985. Toxicity of insecticides. 2nd edn, Plenum Press, New York.
Murty AS 1986. Toxicity of pesticides to fish. vols 1 & 2, CRC Press Inc, Boca Raton, FL.
NSW EPA 2000. Analytical Chemistry Section, Table of Trigger Values 20 March 2000, LD33/11, Lidcombe, NSW.
Reish DJ, Kauling TJ, Mearns AJ, Oshida PS, Rossi SS, Wilkes FG & Ray MJ 1978. Marine and estuarine pollution, Journal of the Water Pollution Control Federation 50, 1424-1469.