Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Ann Hamblin, Bureau of Rural Sciences, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06748 5
Soil and land pollution (continued)
Land is used for disposing of a range of domestic and industrial waste. This is dealt with in the Human Settlements Theme Report.
How much agricultural pesticide goes where? [L Indicator 6.6]
Government responsibility for decisions on agricultural chemical use and practices is split between a number of bodies. The National Registration Authority is responsible for registration of chemicals, while state and territory agencies are responsible for actual control over use. Inter-governmental agreement on standards and policies are overseen by the Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ). This body has developed a National Strategy for the management of agricultural and veterinary chemicals (ARMCANZ 1998) with the goal of developing best practice management for ecologically sustainable and socially acceptable food and fibre production in the use of agrichemicals. However, the monitoring and assessment of practices is not supported either by legislation or by government funding at present.
Information on agricultural and veterinary chemical usage is not collected on a regular, formal basis across Australia. Herbicides, insecticides, fungicides and a range of animal parasiticides have been routinely used in Australian farming systems for between 20 and 40 years, but often in lower frequencies than in many other countries. Large parts of the grazing lands have not been subjected to any regular spraying, and would be able to make a valid case for being considered 'pesticide-free' if monitoring and reporting were systematically undertaken. The value of such a program has been well demonstrated by the National Residue Survey (details on assessing residues in agricultural commodities are listed).
All forms of pesticide use have increased over the past two decades (see Figure 71). Herbicides form by far the greatest part of the total cost, and are most widely applied, but pose much lower environmental or human health risks in most situations than do insecticides (see Table 36 and PIRI). Herbicides, insecticides and fungicides (plus growth regulants) applied to crops and pastures account for 65% of the total expenditure on agricultural and veterinary chemicals, and animal products (endo- and exo-anthelmintics to control animal parasites, and veterinary products) account for the remaining 35% (Avcare pers. comm.).
Figure 71: Total pesticide expenditure on herbicides, insecticides, fungicides/plant growth regulants, 1987-1997.
Source: ABARE (unpublished data)
Although agriculture is without doubt the largest user of pesticides, significant quantities of herbicides are also used by local councils and road and rail authorities for weed control. ABARE has recently mapped the expenditure on agrichemicals and livestock veterinary materials by farm type, which shows some striking differences among broadacre farming regions, as well as the much larger expenditure on cotton and sugar farms in localised districts. In these districts, and in the grain belt of south-west Western Australia, central and southern Queensland and north-east New South Wales, total expenditure on crop chemicals was estimated at over $50 000 in 1998-99. In contrast, the expenditure in the rest of the mixed farming regions ranges from $5000 to $30 000. In the rangelands and high rainfall grazing districts the expenditure on farm chemicals is under $2000, but livestock chemicals (drenches and veterinary products) range from $3000 to $5000 in additional costs. This work did not include expenditure on horticultural farms, which would increase the total expenditure in irrigated regions of the Murray-Darling Basin, eastern Tasmania, and the east coast regions of the Sydney Basin and wet tropic coast of Queensland. Nevertheless the intensive irrigation and rain-fed cropping regions can be clearly distinguished from both the higher and lower rainfall grazing areas, where expenditure is less than $5000 per farm.
Some industries, notably the wine industry, some orchardists, sugarcane and cotton growers, and some beef producers, have developed self-monitoring systems in recent years as part of their need to satisfy stringent environment and safety standards for certain market outlets. Avcare Ltd has been a catalyst to encouraging good stewardship in agricultural use of chemicals. Some rural industries, local government councils and transport authorities, however, are not so well organised. Demonstrating responsible pesticide management remains an ad hoc and patchy activity, requiring leadership from stakeholders to overcome this.
At present, there are no data available on the proportion of agricultural and veterinary chemical expenditure attributable to local government, transport authorities and conservation agencies.
At the time of writing, the proposed database, to be set up under a joint body of Standing Committee on Environmental Protection (SCEP) and Standing Committee on Agriculture and Resource Management (SCARM) has not received expected funding support, nor have all the consulted stakeholders agreed to it. A feasibility study has been undertaken to identify methods for obtaining estimates on a national and/or catchment scale, and concluded that a national scale was feasible with regular repeats every two years. Catchment scale databases would be much more expensive. The Bureau of Rural Resources is currently undertaking a pilot study of such a database.
The dollar value is too crude a measure to be able to assess the impact of pesticides on the environment. While the value continues to increase this should not be construed as an ever-increasing pressure, since many older, cheaper chemicals were less specific in their target action, and were used widely simply because they were cheap (when out of patent protection). Similarly, to replace a dollar indicator with weights or volumes of active ingredient will not provide adequate information on the environmental impact of agricultural chemicals, as the examples of two widely used products, one a herbicide and one an insecticide show (see Box: 'Herbicides and insecticides are not the same').
The word 'pesticide' is often used very broadly to describe any agricultural chemical, but among the thousands of chemicals produced, groups of compounds differ, designed for different purposes. A very widely used example of a herbicide and an insecticide are described below to demonstrate the differences in two such groups.
Glyphosate is a broad-spectrum, non-selective herbicide that is used as a 'knock-down' spray. Knock-down herbicides are the basis of 'direct-drill' (and no-till) systems of crop production which are practised across 5-10 million hectares per year.
Glyphosate kills virtually all annual and perennial plants, but has very low toxicity to other life forms, is adsorbed on soil and then safely metabolised by soil organisms. It was the subject of a special review by the National Registration Authority in 1996 because of reports from Western Australia of toxic effects on frogs and tadpoles. The review found that certain surfactants used in some glyphosate formulations are acutely toxic to tadpoles, but the active ingredient was not harmful. Seventy-five registered products were assessed, and the NRA has redefined the surfactant formulations for products that will be used near drains, channels, dam margins etc.
Glyphosate is regarded as a vitally needed herbicide to control aquatic weeds (eg salvinia, and Mimosa pigra) which threaten many waterways. It is used by many government agencies in controlling weeds of national significance.
Endosulfan (C6H6Cl6O3S) is an organochlorine insecticide that has been used in Australia for over 30 years. In 1999, the NRA undertook a very comprehensive review of it. It has many attributes that make it very valuable to agricultural crops that suffer from sucking, boring and chewing insects, especially cotton, stone and pome fruit, vegetables, cereals, lupins, peanuts, sunflowers, pastures and tree crops.
Other organo-chlorine insecticides (dieldrin, chlordane, aldrin etc) have been withdrawn from use. Endosulfan has a different chemistry, with low toxicity to beneficial insects and no evidence of long-term health effects on people. However, although it volatilises from soil in 1-2 days, and is totally dispersed by 3-6 months, runoff and soil erosion can transport particles containing endosulfan into streams and other water bodies.
The most serious consequences of endosulfan are to aquatic life forms. It is acutely toxic to fish at very low concentrations (<1rains and high water flows bring endosulfan into water with large quantities of soil.
The review concluded that endosulfan should not be withdrawn from use in those industries where its removal would only lead to the substitution of other insecticides that would be likely to have more harmful effects.
However, the review has not closed, and the NRA has regulated a number of changes to the registered use and operational constraints on use of endosulfan in the cotton industry. These include no more than three sprays per season; notification of neighbours; and, from 1999 onward, only spraying between November and January.
For further information see NRA's website.
While open water presents an immediate problem to health and aquatic organisms, groundwater contamination will persist for very long periods, and may affect future generations as well as current users.
The pathway depends on the degree to which the chemical is inactivated in soil by undergoing a chemical transformation such as hydrolysis or sorption, or whether it combines with organic matter and clay in forms where the activity is not altered. In this case the pesticide will still affect sensitive organisms, even though now adhering to particles that can be transported by overland flow or through preferred pathways in the soil profile (Kennedy et al. 1995).
Certain chemicals, such as atrazine and endosulfan, are regularly found in catchments where pesticides are applied to bare-soil cropping systems, as the result of runoff events that occur unexpectedly shortly after spraying. The problems are worst for summer-grown crops in regions of summer-dominant rainfall and irrigation (National Symposium on Pesticide Management in Catchments 1998, LWRRDC/CRDC/MDBC 1997).
Figure 72: Off-target pathways of agricultural pesticides.
If high intensity storms occur at a time when there is bare soil in irrigated paddocks, it is impossible to prevent substantial erosion and runoff. This is therefore a particular problem in irrigated cotton and vegetable production systems in the north-eastern tributaries of the Darling River, such as the McIntyre, Gwydir, Namoi, Macquarie, Bowen, Condamine, and Balonne. In these catchments there has been an increase in the number of chemicals detected in water at monitoring sites since 1995, following the end of the severe drought of the early 1990s and the expansion in cotton planting. However, the levels of endosulfan detected in water have been decreasing since the early 1990s, as education on management and regulatory control of this important but dangerous chemical has improved (Spence and Titmarsh 1998).
In most other farming systems conservation tillage (maintaining a trash cover) and 'chemical fallowing' in inter-row areas of orchards and vineyards used to maintain a surface cover reduces the risk of erosion. The extent to which this is achieved depends on the degree to which cover retention is seen as a high priority. Recent survey estimates are about 30% of broadacre crop land has stubble cover after planting (ABARE 2000), and grazed pastures maintain over 80% cover except in drought seasons, when the cover level may drop to less than 30%.
Detailed investigations of groundwater quality have been undertaken by Commonwealth and State agencies in selected key aquifers from 1990 to the present, under the Australian Groundwater Quality Assessment Project (Bureau of Rural Sciences 1997, 1998, 1999, 2000). Groundwater provides 20% of the nation's total water requirements, but this rises to 100% in some remote mining settlements. This project is of great importance in providing baseline information on the status of groundwater, both in terms of natural contaminants that occur as the result of hydro-geological processes, and as a record of pollutants that can only have arisen as the result of inappropriate anthropogenic activities. Groundwater that underlies populated areas is frequently used for domestic and town water supplies, and for irrigation. However, it may become contaminated by agricultural and industrial activities with far-reaching effects on whole communities, if aquifer water quality is not monitored.
Figure 73 summarises the extensive data that has been published from nearly 300 bores and many thousands of analyses in these aquifers to date. The most important conclusion that comes from this work is that any contamination by pesticides is very low in nearly all bores, and the most frequent occurrences are s-triazine type herbicides, which have a very low ability to bind with soil, but also a short half-life. While the Australian Drinking Water Guidelines state that drinking water should contain no pesticide, the record to date is satisfactory (NHMRC/ARMCANZ 1996). Of the low percentage of exceedances found, nearly all are at very low concentrations, well below any concentration with environmental or health concern. Three of the aquifers have no detectable pesticides.
Figure 73: Proportion of all bores in surveyed aquifers that have any detectable pesticide.
Sources: (Bureau of Rural Sciences 1997, 1998, 1999, 2000)