Copper, a metal used as a fungicide in agriculture, particularly in organic farming, has raised concerns over its potential effects on the environment and human health. Many amateur gardeners use copper to protect their crops from diseases, while it is also widely used in both organic and conventional farming. Copper has been applied in agriculture for over a century, especially to combat downy mildew in vineyards, which is why it is often referred to as "Bordeaux mixture." Its use has since expanded to fruit trees, vegetable crops, and large-scale farming, serving as an alternative to synthetic pesticides. As a heavy metal, copper (Cu) has sparked controversy due to its possible impacts on health and the environment. In 2025, the French National Agency for Food, Environmental and Occupational Health Safety (Anses) re-evaluated copper-based products and tightened their usage conditions. Copper is naturally present in soil, with concentrations varying based on the geological composition of the area. Natural sources include atmospheric deposits from rock erosion, volcanic activity, or forest fires. Soil concentrations of 10 to 30 mg of copper per kilogram (or ppm) are generally considered natural and necessary for the functioning of living organisms. In plants, copper helps with photosynthesis and respiration, while in animals, it supports immune function and protects against oxidative stress. Human activities are also a major source of copper in soil. Industrial and mining operations, transport, especially from diesel vehicles, and waste incineration contribute to atmospheric copper deposition. In agricultural soils, the main source of copper is the application of animal manure, which accounts for about 53% of the total annual copper input. This is partly due to the use of copper-rich feed supplements in some livestock farming to promote growth. Phytosanitary treatments, used to control plant diseases, contribute about 34% of the total annual input. These practices, concentrated in vineyards, can lead to significant local accumulations of copper. Soil concentrations above 100 ppm are often seen as a sign of heavy human influence. Copper tends to accumulate in the top layers of soil, where it can remain for a long time. Vineyards, in particular, show this over time, with some plots having been treated for over a century. In the early 20th century, copper inputs could reach as high as 50 kg per hectare annually, but regulations have since reduced this to a maximum of 4 kg per hectare. Many winemakers have adapted by reducing the amount of copper they apply, although it remains challenging to eliminate it entirely, especially in organic farming where synthetic pesticides are not allowed. The average copper concentration in French agricultural soils is around 13 ppm, while in viticultural areas, it is closer to 70 ppm, though this varies depending on the history of the land. The impact of copper on soil organisms is a growing area of study. Earthworms, a key indicator species, show signs of reproductive issues and high mortality at soil concentrations of 94.6 ppm and 113 ppm, respectively. While such levels are rare in most agricultural soils, they can be found in older vineyards with significant copper buildup. Other soil organisms, such as nematodes and collembolans, appear more resistant, with effects observed only at much higher concentrations. Microorganisms also show varying tolerance to copper, with fungi being more sensitive than bacteria. However, not all fungi respond the same way, making it difficult to establish a single threshold for ecological disturbance. The complexity of copper's environmental impact lies in its different chemical forms, which affect how accessible it is to organisms. Some copper is tightly bound to soil components, such as organic matter or minerals, making it less available, while other forms, like dissolved copper ions, can be more easily taken up by living organisms. Factors like soil acidity and organic matter content influence this bioavailability. Practices such as adjusting soil pH with lime or increasing organic matter through cover crops can help manage copper levels. Researchers are also exploring the use of bioindicators, such as land snails, to better understand copper's actual impact on ecosystems. In recent years, scientists have investigated using microorganisms to mitigate copper contamination in heavily affected soils. Certain bacteria, like Methylosinus trichosporium and Bacillus subtilis, can absorb and store copper, reducing its toxicity. Other bacteria, such as Pseudomonas putida, help plants take up more copper from the soil, aiding in its removal. Aquatic plants, known as macrophytes, are also being used to trap pollutants in runoff water, reducing copper levels by up to 45%. These bioremediation methods offer promising solutions for managing copper contamination. While uncertainties remain due to the diversity of soil conditions and the difficulty of setting universal thresholds, the effects of copper under current usage levels appear limited. A careful and reasoned use of copper is essential, and bioremediation techniques may be valuable in soils where copper levels become too high.