Poor Management of Animal Wastes

Industrial animal production is the largest growth sector in both developed and developing country livestock production systems. Over the five year period between 1991 and 1996 there was an estimated 37% increase in the sector, which then accounted for around 43% of global meat production, and over 60% of the global egg production. | Excessive Nutrient Levels in Soils Pollution of Surface and Groundwater Heavy Metal Contamination of Manure Environmental Assessment: Pressure State Response Indicators Policy Pressures and Policy Options

The potential problems will be most significant in the developing world, where demographic patterns and rural-urban migration are resulting in rapidly expanding urban centres largely dependent on industrial production for animal proteins.

The distribution of these industries is determined by infrastructure and access to market. As a result there is a tendency to concentrate industrial production and processing sites in urban and peri-urban areas, and in the immediate surrounding rural areas.

The industry depends almost entirely on the provision of external feed and other inputs, while occupying little land area, and as a result has the potential for generating large volumes of waste products that are in excess of the natural absorptive capacity of the environment. The management of these concentrations of waste products poses similar environmental management problems to the treatment and disposal of urban waste.

The biggest problem is the treatment and disposal of manure. In general it is uneconomical to transport wastes beyond 15 kilometres, limiting the potential for positive benefits in terms of use as an input to cropping systems. The problem is often compounded by the low costs (often subsidised) and ease of use of mineral fertilisers, reducing the demand for organic manure.

Excessive Nutrient Levels in Soils

While limited applications of manure are a key component of maintaining soil fertility in mixed and arable systems, excessive loading of manure onto limited land areas results in imbalances in plant nutrients, leading to changes in natural vegetation systems and affecting the potential of cropping systems. At higher levels, N, P and K can all build up to toxic levels, limiting plant growth and species potential. Poorly treated and excessively fresh manure can damage crop growth through acidity.

However, in most cases, the problems of land based disposal of manure are not restricted to the soils, direct run-off and leaching result in pollution of surface and ground water.

Pollution of Surface and Groundwater

Both direct drainage of manure to surface water and leaching from saturated soils affects water quality. Nitrates are leached off into groundwater resulting in human health hazards; high levels have been associated with increasing risks of contracting methaemoglobinaemia (blue baby syndrome). Although in most cases there will be existing or planned treatment works for domestic water supplies from surface water which could be upgraded to deal with the impacts of manure, groundwater treatment is less likely to be directed to the removal of nitrates and hence would require major investments to deal with this source of pollution.

The major concern for the natural environment is the impact of run-off and leaching of nitrogen and phosphates which can directly lead to eutrophication anf biodiversity loss in aquatic ecosystems. However, this impact on the natural environment can itself result in further human health risks, as a common result of eutrophication is the excessive growth of blue-green algae (notably Microcystis spp.). This algae produce a number of toxins which, if ingested, can cause liver damage to both human and animal populations.

Heavy Metal Contamination of Manure

Feed additives often contain traces of heavy metals, added as supplements and growth stimulants. These elements are often added in excess, and are excreted in manure. As a result there is the potential for a build-up of these elements within the environment, with potentially negative environmental impacts.

Further details of these problems are given under the use of Chemical Inputs.

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