Agricultural Arsenic

Management of arsenic in agricultural soils and water

by Arslan Ahmad, KWR Water Research Institute, Nieuwegein, The Netherlands Prosun Bhattacharya, KTH Royal Institute of Technology, Stockholm, Sweden

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Arsenic is a metalloid which is widely found in natural soils and water on Earth. It is a proven carcinogen for humans and exposure to high concentrations of arsenic (As) should be avoided.

The presence of arsenic at elevated concentrations in groundwater is not only dependent of the concentration of As in the soil, but on the constituents and environmental chemistry of the soil that influence its speciation and mobility. The mobility of arsenic in the soil is controlled by pH, redox conditions, biological activity and adsorption/desorption processes, especially on the Fe – and manganese (Mn) oxyhydroxides. The presence of arsenic in food transferred through the water-soil-crop route has triggered a potential risk of environmental hazard to human health through dietary pathway and a concern for food safety worldwide since past two decades. The recently completed European Water JPI project “Evaluation and Management of Arsenic contamination in agricultural soil and water (AgriAs)” reviewed European databases to develop recommendations for the sustainable management of arsenic in agricultural soils and water. KWR Water Research Institute joined hands with other organisations from five European Union countries to develop knowledge in this project.

In agricultural soils of Europe, arsenic anomalies are linked to both natural geochemical baseline concentrations and anthropogenic origin. We focused on two arsenic contaminated sites: a French site and a German site. The French study site is an area where chemical ammunition from World War I were dumped. The German site is characterised by 800 years of mining and ore processing. We organised stakeholder workshops in France and Germany to interact with local farmers, authorities and researchers to develop understanding of the arsenic issue. Recommendations were made, especially for Saxony where local authorities annually update recommendations on how to manage contaminated soils used for agriculture and gardening.

“the most commonly used technologies for water treatment are precipitation, adsorption and membrane processes”

The exposure of people to arsenic in certain areas is equal to or exceeds the exposure which is considered to be a low-risk level. Therefore, reduction of exposure is appropriate in these areas. We recommend that the authorities should make efforts to keep As concentrations as low as reasonably possible in food and drinking water by applying effective soil and water treatment processes.

Treatment methods

Treatment methods for soil can be divided into two main categories: methods for the removal of pollutants (soil washing, in situ soil flushing, electrokinetic treatment, phytoremediation, biological treatment) and methods for the immobilisation of pollutants (solidification, vitrification, soil amendments/adsorbents). The most commonly used technologies for water treatment are precipitation, adsorption and membrane processes. These technologies meet the requirements for sufficient arsenic removal efficiency for drinking water. Thus, particular attention should be paid to the environmental sustainability of the methods as well as the economic aspects. Technologies, which require a minimum amount of chemicals and which minimise the amount of secondary waste are the most favourable when selecting the treatment methods. The purification technology should be chosen case-specifically considering the characteristics of the water to be treated. Technologies requiring a minimum amount of chemicals and minimising the amount of waste are favourable when selecting the treatment methods. Environmental sustainability is expected to play a major role in the current climate change era.

Transfer to water systems

At Verdun site in France, field and laboratory studies focused on the mobility of arsenic, toxicity towards plants and transfer to the water systems. Highly promising results were obtained with microbial and plant bio-indicators of the availability and toxicity of arsenic. The effects of soil amendments on the uptake of arsenic by crops was studied at both French and German sites.

In order to perform a risk assessment of the target sites, the guideline values can be used to compare with measured concentrations. The guideline values give a very generic assessment, which does not take the actual conditions at the site into account. A detailed approach for performing a risk assessment is exposure modelling that enables us to analyse the extent and the causes of the risk, and would further help to decide the strategies for risk reduction through the choice of appropriate method for remediation. Development of risk assessment models is recommended so that the physical and chemical form of arsenic in the releasing and receiving environments can be included. This will allow the effect of important environmental factors, such as redox conditions that could be taken into account.

Exposure models, on a general note, are used to calculate the exposure of a chemical for assessments of the effect of a chemical on human health. Different models do this through different methods, but overall, they take into account exposure to humans from different pathways set to certain parameters. On the contrary, exposure models from the USA, incorporate pathways that range from intake of soil, intake of vegetables, grains, intake of meat and milk, intake of water, intake of fish, inhalation of dust and dermal contact, and they use parameter that suit consumption and situations relevant to USA (MMSOILS, 2007). For As, pathways that are most interesting and cause the most impact on human health have been identified to be ‘intake of water’ and ‘intake of As contaminated plants’, (specifically grains and leafy vegetables).

Risk assessment

To perform a risk assessment for As in European sites, it would be important to use models set to European parameters. However, most of the existing models in Europe mostly focus on residential land use and not specifically agricultural land use. There is also a significant data gap on the consumption pattern of different types of crops. Therefore, for performing a health risk assessment of arsenic in agricultural lands of Europe, there is a lack of exposure models that will give site-specific results taking into account different exposure pathways, set to European standards.

The AgriAs risk assessment model is specific to the inorganic arsenic and the results generated from the model are more site-specific that focus on:

  • Environmental exposure pathways including soil intake, water intake, dust inhalation, dermal contact
  • Consumption pathways which include consumption of different plant products grown in an agricultural region, such as leafy, non-leafy and root vegetables, fruits as well as grains
  • Consumption of secondary foods produced in an agricultural region like meat, milk, eggs, and fish

If the site concentrations are unavailable, the user can use the ‘Transfer Factor’ method and use the measured concentration of arsenic in soil, and the predefined transfer factors given in the AgriAs model’s plant index. This will give indicative site-specific results, but might not be as specific as using the measured site concentrations. If site concentrations of the plant, or the transfer factors are not available, the user can choose a third method of using ‘EFSA database for inorganic arsenic in food in Europe’. This makes the model use generic concentrations of arsenic in food in Europe. This will generate generic results. Due to these various input options, even if there is less site data available, the model can still generate some basic results to work with.

“highly promising results were obtained with microbial and plant bio-indicators of the availability and toxicity of arsenic”

A comprehensive risk assessment would thus assist us to reduce the risks of exposure through different pathways, using the Agri-As exposure model.

No data were available in the European-wide mapping programmes from two countries: Moldova and Turkey, and Romania was missing from the GEMAS survey and Norway from the LUCAS survey otherwise carried out on the European level. There is no up-to-date data on As concentrations in European groundwater related to agricultural sites. More data should be collected from surface waters if they are in the same watershed to As-rich soils in small catchment areas. Data on the transfer of arsenic in the food chain (from soils, to crops, to animals and to food products) are lacking for a number of important foods.

Future recommendations

It is recommended that the future research should focus not only on arsenic, but on the interaction of different contaminants in soil and water systems. In our test sites, and in many other arsenic contaminated areas according to our experience and the literature, other metals and organic contaminants are present in concentrations that imply risks to health and the environment.

The effects of emerging contaminants like medical residues, hormones, pesticides, herbicides and microorganisms on the behaviour of arsenic are poorly understood. Other contaminants are also important with regards to amelioration techniques for soil, as the immobilisation of arsenic can cause other contaminants to become more mobile. The European Commission withdrew the drafts of the European Soil Protection Directive in 2016 but the results from our project show that the need for coordinated management of the problems of As-contaminated soils remains. This could be achieved with guidelines and regulations developed in close cooperation with the stakeholders both in the national and at the EU level. Soil contamination by arsenic can be caused by various sources: e.g., mining and processing of sulphide ores, residues of weapons, mineral occurrences, dust from smelters and pesticides. Soil contamination has consequences not only for agricultural products but also for the contamination of groundwater and air. n

“it is recommended that the future research should focus not only on arsenic, but on the interaction of different contaminants in soil and water systems”

Author Details

Arslan Ahmad, KWR Water Research Institute, Nieuwegein, The Netherlands Prosun Bhattacharya, KTH Royal Institute of Technology, Stockholm, Sweden

Arslan Ahmad is an internationally oriented water professional and a leading Research Scientist at KWR Watercycle Research Institute, with particular focus on the removal and recovery of (trace) metals from drinking water and aqueous waste streams. He is an elected member of the Executive Management Committee of the IWA Specialist Group on Metals and Related Substances.

Dr Prosun Bhattacharya is a Professor of Groundwater Chemistry at KTH Royal Institute of Technology.
He has been elected as the chair of the IWA Specialist Group Metals and Related Substances in Drinking Water. Based on his global engagements in the field of arsenic research he has been honored with the title as the Fellow of the Geological Society of America in April, 2012 and has been conferred with the title of the fellow of the International Water Association (IWA Fellow) in September 2018. He is the Editor in Chief of the Elsevier Journal Groundwater for Sustainable Development.

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