Chlorine and its Oxides - Chlorate & Perchlorate Review

Summary: 
The use of chlorine compounds such as sodium and calcium hypochlorite and chlorine dioxide for disinfection (herein referred to as chlorination or chlorine disinfection) leads to chlorate (ClO₃^-) and perchlorate (ClO₄^-) residues in plant tissue. Applications of chlorination include irrigation system disinfection to reduce algae and bacterial blockages, removal of potential water-borne plant pathogens, disinfecting process water (e.g. for use in hydrocooling), cleaning/disinfecting machinery, surfaces and harvest equipment, and disinfecting water used in the post-harvest washing of produce to reduce contamination with human pathogens such as Salmonella spp.. The European Food Safety Authority (EFSA) is currently reviewing the Maximum Residue Levels (MRLs) of chlorate and perchlorate in foods. Tighter legislation will result in some growers unable to comply without changing their current water treatment practices.

The review will focus on the sources and fate of chlorate and perchlorate assimilated by horticulture produce, including potatoes. The review will also assess techniques that levy payers can adopt to reduce residues either by manipulating existing systems, or adopting a hydrogen peroxide (H₂O₂) based treatment system. It is important to consider the practical feasibility for levy payers whilst maintaining microbial integrity and high levels of food safety, avoiding any unintended consequences.

Aims:

To produce a comprehensive and critical literature review on the use of chlorine and chlorine derived compounds for disinfection in horticultural production systems pre-, during, and post-harvest of fresh produce and for potato washing.

To gain insight into the sources and fate of chlorate and perchlorate residues and to evaluate ways of reducing them by manipulating existing chlorination systems

To evaluate hydrogen peroxide based disinfection systems for utilisation in various horticulture production systems and in potato washing. 

To identify actions that levy payers can undertake to mitigate against chlorate and perchlorate exceedances in edible fresh produce and in washed raw potatoes destined for packaging or further processing.

To carry out knowledge exchange with levy payers and others in the horticultural industry

To to identify priority R&D opportunities in this work area for future levy funding to target.

Objectives:

Objectives to be met are as follows:

1. To provide an overview of chlorine chemistry relevant to its use as a disinfectant in horticultural systems (and potato washing) and to assess factors influencing the production of unwanted by-products, focussing on chlorate and perchlorate. 

2. To investigate the source of, and the mechanism by which chlorate/perchlorate is taken up by horticultural plants.

3. To investigate and critically evaluate the fate, bioaccumulation, assimilation and tolerance mechanisms of chlorate/perchlorate in different horticultural plants.

4. Investigate the amount of chlorate/perchlorate assimilated by fresh produce and potatoes through contaminated process and wash water.

5. Identify opportunities for levy payers to manipulate existing chlorination systems to reduce chlorate/perchlorate residues whilst maintaining product quality and consumer safety, including the potential for reducing dose rates.

6. Evaluate the advantages/disadvantages of the use of hydrogen peroxide as an alternative to chlorination in irrigation/wash water and consider the practical aspects of conversion.

7. To recommend areas for further Research & Development and Knowledge Transfer work

8. To prepare an article for AHDB Grower and to give presentations at AHDB events/workshops.

Benefits of project:

 (a) Levy Payers 
Growers will be able to make informed decisions about which disinfection system is most suited to their operation, and how to run it to reduce unwanted by-products such as chlorate and perchlorate. Information will be provided on the effectiveness of hydrogen peroxide based disinfection systems to enable growers to decide on their feasibility as an alternative to chlorination. Ultimately this report should help growers to achieve lower levels of chlorate and perchlorate residues to conform with potential changes to MRLs imposed by the European Commission, whilst also satisfying retailers by maintaining high standards of food quality and safety.  

(b) Consumers    
Reducing the chlorate and perchlorate content of fresh produce (and potatoes) has numerous health benefits to the consumer due to the effect of these residues on functioning of the thyroid. Perchlorate is an endocrine disruptor, and pregnant women, foetuses, and new borns have the greatest potential for adverse health effects. This review aims to assess methods of reducing chlorate and perchlorate levels in the food reaching consumers whilst also maintaining adequate microbial decontamination of potential human pathogens. If food produce does not meet the new modified MRLs it will not make its way onto the market, limiting potential availability of certain foodstuffs to the general public.

(c) Environmental benefits        
Chlorate and perchlorate are relatively stable residues which can persist in the environment, including in water sources. If current chlorination systems can be modified to reduce the amount of chlorine required for decontamination then less energy will be required for its production and for transport, ultimately reducing the carbon footprint of the industry. If a system utilising hydrogen peroxide for disinfection is adopted, then it is unlikely there will be any issues with residues as this substance degrades into water and oxygen. If reductions in chlorate and perchlorate can be achieved then the continued practice of water recycling will be supported, thus significantly reducing risks of environmental contamination through disinfectant and/or pesticide use whilst also reducing fresh water usage.