Copper accumulation in soils: environmental impacts and sustainable alternatives

Why is copper at the heart of agricultural debate today?

Copper accumulation in soils has become a major environmental concern in agriculture and viticulture. Used for more than a century in crop protection, copper-based fungicides remain essential for controlling major fungal and bacterial diseases, particularly in vineyards, fruit production and organic farming systems.

However, repeated copper applications can lead to copper accumulation in agricultural soils, potentially affecting soil biodiversity, microbial activity and water quality. As environmental regulations evolve across Europe, the agricultural sector is increasingly seeking sustainable alternatives and strategies to reduce copper use while maintaining effective crop protection.”

Since when has copper been used in agriculture?

The use of copper in crop protection dates back to the late nineteenth century. In 1885, French botanist Pierre-Marie-Alexis Millardet developed the famous Bordeaux mixture, a combination of copper sulphate and lime designed to control grapevine downy mildew.

This discovery marked a major turning point in crop protection. Rapidly adopted across European vineyards, Bordeaux mixture became one of the first fungicides used on a large scale.

Over time, several copper formulations were developed:

• Copper sulphate,
• Copper oxychloride,
• Copper hydroxide,
• Cuprous oxide.

Despite the introduction of numerous synthetic crop protection products during the twentieth century, copper remains authorised in organic farming in many countries, including those of the European Union, under specific conditions and usage restrictions.

Copper in soils: what are the challenges?

Unlike many organic molecules that degrade over time, copper is a metallic element naturally present in the environment that, once applied, does not disappear.

Part of the applied copper is removed through harvested crops or dispersed into the environment, but a significant proportion gradually accumulates in the upper soil horizons.

This characteristic explains why fields with a long history of copper applications, particularly certain European vineyards, sometimes exhibit copper concentrations significantly higher than natural background levels.

However, the actual impact of copper does not depend solely on its total concentration in the soil. Its bioavailability, strongly influenced by soil pH, organic matter content and physicochemical properties, is also a key factor in assessing its potential effects on living organisms and ecosystems.

Copper accumulation in agricultural soils: a European issue

The regions most affected are generally those where copper applications have been carried out for several decades, including:

• Certain wine-growing regions of Italy,
• Spain,
• Germany,
• Portugal,
• Austria,
• Switzerland,
• Major French wine-growing regions:

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Data presented by the Ecotox Network indicate that French vineyard soils may contain several tens, and in some cases several hundreds, of mg Cu/kg in surface horizons.

Is copper a heavy metal?

Copper is generally classified as a trace metal element (TME), sometimes grouped under the broader term “heavy metals” in environmental literature.

It is an essential micronutrient required for the proper functioning of plants, animals and humans when present in small quantities. However, excessive accumulation can lead to toxic effects on many living organisms.

This dual nature makes copper management particularly challenging: essential at low concentrations, copper can become harmful when present at elevated levels, that is, above naturally occurring environmental concentrations and potentially affecting certain organisms.

What are the impacts on soils and biodiversity?

Agricultural soils host a rich biodiversity that is essential for the functioning of agroecosystems. Microorganisms, fungi, earthworms, springtails and nematodes all contribute to organic matter recycling and soil fertility.

As copper concentrations increase, certain biological functions may be affected. Soil organisms are among the first to be impacted by copper accumulation. Several studies have shown that high copper concentrations can affect the reproduction of sensitive species such as earthworms and springtails, while also altering microbial community activity.

Research conducted by Karimi et al. (2021), Imfeld et al. (2021) and the Ecotox Network further indicates that copper accumulation may influence microbial diversity and several key soil biological functions.

Nevertheless, observed effects vary considerably depending on soil and climatic conditions, soil characteristics, environmental factors and the actual bioavailability of copper. This variability explains why risk assessment today relies on a more refined approach than simply measuring total soil concentrations.

Copper and water pollution: a major challenge for aquatic ecosystems

Aquatic organisms are among the biological groups most sensitive to copper exposure.
Following plant protection applications, part of the applied copper can be transferred to surface waters through runoff or through erosion of soil particles to which copper is adsorbed. Most of the exported fraction is associated with solid particles, while a smaller proportion occurs in dissolved form, generally considered the most bioavailable to aquatic organisms.

According to EFSA (2018), Peer review of the pesticide risk assessment of the active substance copper compounds, algae, aquatic invertebrates and aquatic microorganisms are among the most sensitive organisms exposed to copper.

However, the potential impact depends strongly on the physicochemical characteristics of the receiving environment, particularly pH, water hardness and dissolved organic matter content, all of which directly influence copper bioavailability.

In this context, reducing transfers to surface waters has become an important objective of environmental protection strategies and European water resource conservation policies.

Regulatory overview: what does European legislation say?

In response to environmental concerns associated with copper use, the European Union has progressively strengthened its regulatory framework. Since 2018, copper use has been limited to an average of 4 kg of metallic copper per hectare per year, with a maximum cumulative limit of 28 kg over a seven-year period, allowing application rates to be adjusted according to climatic conditions, in accordance with Commission Implementing Regulation (EU) 2018/1981.

This regulatory development aims to preserve the agronomic benefits of copper while limiting long-term accumulation in soils and transfers to aquatic environments.

Assessments conducted by the European Food Safety Authority (EFSA)  have played a major role in this regulatory evolution by identifying risks associated with copper compounds for both terrestrial and aquatic organisms.

Copper is also receiving particular attention within European discussions on agroecological  transition and the reduction of the environmental impact of plant protection products.

Why are agricultural sectors seeking to reduce copper inputs?

The objective is not to challenge the effectiveness of copper. Copper remains a benchmark solution against several major diseases and continues to be a cornerstone of many crop protection strategies, particularly in organic farming.

The challenge is to maintain this effectiveness while reducing the environmental impacts associated with its accumulation.

The main objectives currently pursued are:

• Preserving soil biodiversity,
• Reducing transfers to surface waters,
• Limiting accumulation in historically exposed fields,
• Maintaining agronomic performance, Meeting regulatory and societal expectations.

This approach is fully aligned with the principles of Integrated Pest Management (IPM) and agroecology.

Is copper essential in organic farming?

Although copper remains widely used in several organic production sectors, numerous initiatives are currently being developed to reduce application rates through the combination of agronomic, genetic and biological approaches.

The objective is to preserve the effectiveness of copper while limiting its long-term environmental impacts.  This trend is driving the development of strategies that combine agronomic practices, decision-support tools, biocontrol solutions, basic substances and other complementary approaches.

Alternatives and strategies for reducing copper use

Scientific research converges on one key conclusion: there is currently no single solution capable of fully replacing copper in all agronomic situations.

The most effective strategies rely on combining several complementary approaches:

• Disease monitoring and forecasting models,
• Optimised treatment timing and positioning,
• Improved spray quality and drift reduction,
• Resistant or tolerant varieties,
• Agronomic practices that reduce disease pressure,
• Biocontrol solutions,
• Basic substances,
• Biostimulants.

This systemic approach enables a gradual reduction in application rates while maintaining a high level of crop protection. The objective is no longer to identify a single substitute, but rather to design integrated programmes that combine multiple complementary solutions.

OPSeed75: a complementary tool to support copper reduction strategies

In a context where the agricultural sector is actively seeking solutions to reduce copper inputs, basic substances can be integrated into approaches based on combining multiple complementary agronomic levers.

OPSeed75 fits within this diversification strategy. Its integration into existing crop protection programmes may contribute to efforts aimed at progressively reducing dependence on copper-based applications, alongside preventive agronomic practices, decision-support tools and other biocontrol solutions.

For farms engaged in input reduction strategies, OPSeed75 can therefore serve as an additional tool that strengthens existing programmes when used in combination with preventive agronomic practices, decision-support tools and other biocontrol solutions.

Its use is part of a broader strategy aimed at gradually reducing dependence on copper while preserving the robustness of crop protection programmes.

Towards More Sustainable Crop Protection

More than 140 years after the invention of Bordeaux mixture, copper remains an important tool in crop protection. Its agronomic effectiveness continues to be widely recognised, but its persistence in the environment raises important questions regarding soil accumulation, biodiversity and water quality.

Research conducted by EFSA (2018), the Ecotox Network, and more recent studies by Karimi and Imfeld show that copper risk assessment can no longer rely solely on total copper concentrations measured in soils. Data from Ballabio et al. (2018), Copper distribution in European topsoils, further highlight the importance of historical copper accumulation observed in certain European agricultural regions.

In this context, dose-reduction strategies based on combining multiple complementary approaches appear to be the most promising path forward. Basic substances such as OPSeed75 can contribute to this transition by being integrated into broader crop protection programmes that reconcile agronomic performance, soil conservation and reduced environmental impact.

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