Cadmium has recently returned to the spotlight in France and across Europe. Recent public health warnings concerning excessive population exposure have drawn renewed attention to this heavy metal, long underestimated but now recognised as a major environmental contaminant.
Although public debate has focused primarily on food and agricultural soils, cadmium is also present in many aqueous effluents, with direct implications for industrial operators and wastewater treatment plants. This article takes a closer look at this pollutant to better understand how it can be treated.
A Toxic and Strictly Regulated Heavy Metal
Cadmium (Cd) is a heavy metal with no known beneficial function in living organisms. Its effects on the human body have been documented since the 1950s. Highly toxic in all its forms—including solids, vapours, salts and organic compounds—it is one of the few elements with no known function in either humans or animals.
Cadmium is recognised for its high toxicity, even at low concentrations, and its ability to accumulate in the human body. It is classified as a priority hazardous substance under the European Water Framework Directive.
Cadmium is also classified as carcinogenic, mutagenic and toxic to reproduction. It is recognised as a known occupational cause of lung cancer and is also suspected of contributing to other cancers, including pancreatic, bladder, prostate and breast cancer.
Other effects documented in the scientific literature include chronic kidney damage, bone weakening—including osteoporosis and an increased risk of fractures—and cardiovascular toxicity.
From an environmental perspective, cadmium is:
- non-biodegradable;
- highly persistent;
- capable of bioaccumulating throughout food chains.
These characteristics make cadmium an extremely persistent pollutant and explain the increasingly stringent regulations governing its release, particularly into water.
Water as a Carrier of Both Life and Pollution
Water lies at the heart of a continuous natural cycle, circulating between the atmosphere, soils, rivers and groundwater. This constant movement makes it an essential carrier of life, supporting both ecosystems and human activities.
However, this transport function has another consequence: water can also become a carrier of pollution. When it comes into contact with contaminants—particularly persistent pollutants such as heavy metals—it disperses them throughout the environment, sometimes over long distances and extended periods.
Unlike some organic pollutants, persistent substances such as heavy metals and PFAS do not degrade. They accumulate in soils, migrate slowly into groundwater and may continue circulating for years or even decades.
In this context, managing water pollution cannot rely solely on dilution or the passage of time. Pollutants must be captured and removed, ideally before they become permanently embedded in the water cycle.
Recent Developments Have Brought Cadmium Back into Focus
French health authorities have recently warned of significant population overexposure to cadmium, primarily through food. For example, the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) published a report in late March urging the French government to take action on cadmium pollution.
These developments have renewed attention on this heavy metal and on phosphate fertilisers, which are produced from geological deposits that may naturally contain high levels of cadmium.
Although public debate is largely focused on the food chain, the situation highlights an essential point: cadmium circulates between soils, water and ecosystems. Because it is both persistent and mobile, it can enter living organisms and accumulate within them.
Cadmium in Industrial Wastewater: A Technical Reality
Alongside these diffuse sources, cadmium is also found in several types of industrial effluent. It may be present in wastewater generated by:
- non-ferrous metal production;
- surface treatment and electroplating;
- battery manufacturing, particularly older Ni-Cd technologies;
- chemical and pigment manufacturing;
- certain waste treatment processes.
In these environments, cadmium is generally present either in dissolved form as Cd²⁺ ions or in particulate form, depending on the physicochemical conditions of the effluent.
Why Is Cadmium Found in Industrial Effluents?
The presence of cadmium in industrial wastewater is primarily explained by its natural association with other metals and its historical use in certain industrial processes.
From a metallurgical perspective, cadmium is often present as an impurity in zinc, lead and copper ores. During extraction, refining or surface-treatment operations, it may be mobilised and transferred into process or rinse water.
Cadmium was also widely used in a range of industrial applications, including nickel-cadmium batteries, certain pigments and specific anticorrosion surface treatments. Although these uses have declined significantly, they remain present in certain industrial sectors and older facilities.
Cadmium may also enter wastewater indirectly through the treatment of industrial waste or the leaching of metal-containing residues. In such cases, it is released in dissolved form and enters industrial water circuits.
Ultimately, cadmium is rarely the main pollutant present in an effluent. Instead, it is generally a persistent trace metal that is difficult to remove completely and enters wastewater through industrial processes or the raw materials used.
An Existing Regulatory Challenge for Industrial Operators
Unlike some emerging pollutants, cadmium is already subject to strict controls in industrial discharges. By classifying it as a priority hazardous substance, the European Union aims to eliminate its discharges, emissions and losses.
Article 16 of the Water Framework Directive establishes a legal and methodological framework for prioritising substances that pose a risk to aquatic environments. Within this framework, Decision 2455/2001 established a list of priority substances, some of which are considered hazardous. Discharges, emissions and losses of these priority hazardous substances were to be progressively phased out within a 20-year period.
Regulated industrial facilities must comply with extremely low discharge limits and, in some cases, zero-discharge requirements. In practice, physicochemical treatment processes allow most industrial facilities to remove a significant proportion of the cadmium present in their effluents.
However, consistently achieving the very low outlet concentrations required for regulatory compliance remains particularly challenging.
Solutions for Treating Cadmium in Water
Cadmium treatment in industrial effluents has historically relied on well-established physicochemical processes.
Chemical precipitation remains the most widely used method. It involves converting dissolved cadmium into insoluble compounds, generally hydroxides, which can then be separated through settling. This treatment is often combined with coagulation and filtration steps to improve solid–liquid separation.
These solutions are effective at removing high cadmium concentrations, but they reach their limits when discharge requirements become more stringent or when the wastewater matrix is particularly complex.
Limitations of Conventional Treatment Processes
At low concentrations, the limitations of conventional processes become more apparent. Chemical precipitation becomes less effective because part of the cadmium remains soluble and the chemical equilibria are highly dependent on pH.
The presence of complexing agents or other metals can make treatment even more difficult by maintaining a fraction of the cadmium in solution.
Under real operating conditions, these constraints make it difficult to maintain stable performance over time. Variations in wastewater composition or production conditions may be enough to cause occasional exceedances, even in otherwise well-controlled treatment facilities.
In such cases, membrane technologies such as nanofiltration or reverse osmosis may be used to provide additional treatment. However, these technologies involve greater operating constraints and significant energy costs. They also generate a concentrated waste stream—the membrane filtration concentrate—which must itself be managed.
Faced with these limitations, adsorption processes are attracting increasing interest. They can directly capture residual cadmium ions from solution, particularly at low concentrations where conventional treatments become less effective.
Their main advantage lies in their ability to stabilise treatment performance, even when the contaminant load or wastewater composition varies.
Technical Apatites for Cadmium Treatment
Certain mineral materials offer particularly valuable properties for this purpose. Apatites, for example, have a natural affinity for heavy metals and can durably bind cadmium through combined adsorption and precipitation mechanisms.
Their affinity for metal ions enables the long-term immobilisation of contaminants during water treatment. This approach opens the way to more robust treatment solutions that are better suited to current compliance and performance requirements.
By developing technical apatites specifically designed for water treatment, BIOHAP provides high removal efficiency for trace cadmium, complementing existing treatment technologies.
This approach can be readily integrated as a polishing step downstream of physicochemical treatment processes to capture residual concentrations that are otherwise difficult to remove.
Column trials conducted with apatite on cadmium-containing effluents demonstrate this performance. With an initial concentration of approximately 1.3 mg/L, outlet concentrations were maintained below 5 µg/L over a broad operating range, corresponding to a removal efficiency greater than 99%.
These results confirm the ability of the media to treat cadmium effectively, including at low concentrations where conventional treatment processes reach their limits.
This approach provides an additional safeguard for regulatory compliance while improving treatment stability when wastewater conditions vary.
By specifically targeting low residual concentrations, apatite-based solutions address the limitations of conventional processes and provide a relevant alternative for industrial operators facing increasingly stringent heavy-metal discharge requirements.
Conclusion
Cadmium currently lies at the intersection of several major challenges: public health, environmental protection and industrial wastewater management.
While recent developments have highlighted population exposure through food, cadmium also remains a contaminant in certain industrial effluents and is already subject to strict regulatory requirements.
Controlling cadmium discharges therefore represents a concrete operational challenge for many industrial facilities. Treatment solutions must be effective and stable while remaining compatible with increasingly demanding operational and regulatory constraints.
For a comprehensive comparison of polishing solutions for trace metal pollution such as cadmium, read our article: Comparison of water treatment solutions for trace heavy metals.