The Use of Sulphuric Acid on Potatoes
Why do We Use Sulphuric Acid on Potatoes?
The application of sulphuric acid to growing potato plants is carried out for the following reasons:
- Killing off the shoots (haulms) of the potatoes makes mechanical lifting of the tubers at harvest very much easier.
- Killing off the haulms also makes the plant move resources to the tubers so giving them a growth burst prior to harvesting.
The use of this chemical is strictly controlled, with stringent conditions being placed on those who use it.
What is a Commodity Substance?
Sulphuric acid is approved as a Commodity Substance. These are chemicals which have a variety of non-pesticidal uses, but which also have minor uses as pesticides. If such a substance is to be used as a pesticide, it requires an approval under COPR and is granted an approval for use as a pesticide, which is subject to the general Conditions for Use set out in Schedule 3 of COPR. These conditions require any person who uses a pesticide to take all reasonable precautions to protect the health of human beings, creatures and plants, to safeguard the environment and, in particular, to avoid the pollution of water. Advice to users on how to meet their responsibilities under this legislation is given in the statutory Code of Practice for Using Plant Protection Products (replaces "Green Code"). This is a statutory Code of Practice and whilst failure to follow this guidance does not render a person liable to prosecution such a failure is admissible in evidence in any proceedings brought against a person.
For information on future changes to the approval of sulphuric acid and other commodity substances please see below.
Sulphuric acid, as with any other agricultural pesticide, can only be used by operators who have received training and hold a certificate of competence. Certificates of Competence are issued by the N.P.T.C. (formally known as the National Proficiency Tests Council). The use of sulphuric acid is also controlled by the Control of Substances Hazardous to Health (COSHH) regulations.
Agricultural Use of Sulphuric Acid
Sulphuric acid currently has approval under the Control of Pesticides Regulations 1986 for use as an agricultural desiccant on potato, bulbs, corms and peas.
Its approval, like that of all pesticides, is supported by a dossier of data, including amongst other things, information on its effect on the environment and non-target species, its safety in use and details of any residues it may leave. Such dossiers are scrutinised by the independent Advisory Committee on Pesticides, which makes recommendations to Ministers on whether a pesticide can be used safely and, if so, under what conditions. If Ministers approve the use of the pesticide, the requirements for ensuring the safe use appear on its ‘approval schedule’; and where a formulated product is to be used, is specified on the product label. The Commodity Substance Approval for sulphuric acid is one means by which farmers and farm workers are provided with specific advice on the safe handling and use of this pesticide.
The Health and Safety Executive (HSE) previously produced a Guidance Note on sulphuric acid entitled ‘Chemical Hazard Alert Notice Sulphuric Acid Mist (CHAN 25). However, all Chemicals Hazard Alert Notices (CHANS) have now been suspended. Those seeking advice on substances for which a CHAN had previously been issued should follow the same approach as they would for any other hazardous substance, e.g. apply the CHIP and COSHH regulations. Further guidance and links are available at:
www.hse.gov.uk/pubns/chan25.htm
A Code of Best Practice for the Use of Sulphuric Acid is available from the National Association of Agricultural Contractors.
Spraying with Sulphuric Acid
Farmers are only allowed to spray sulphuric acid if they have the necessary certificate of competence in the use of the equipment required for its application. Most spraying is therefore done by specialised contractors.
Amongst the specific conditions laid down for the use of sulphuric acid as an agricultural desiccant, operators are instructed that, before spraying takes place, notices must be posted on adjacent roads and paths warning passers-by and drivers of vehicles of the time and place of the intended application and of the possibility of hazard.
Notices must be kept in place for at least 96 hours.
In addition, at least 24 hours written notice of the intended operation and the possibility of a hazard must be given to occupants of any premises and to the owner, or his agent, of any livestock or crops within 25 metres of any boundary of the land intended to be treated. These conditions are outlined in the copy of the commodity substance approval of sulphuric acid.
Effects of Sulphuric Acid in the Environment
The application of sulphuric acid may result in charring of the soil and reduction of the pH in soil and water (if there is contamination of adjoining surface water by spray drift). The effect of an application on soil pH is not that large; it leads to a reduction of about 0.2 pH points. The compound is not persistent and dissipation and the buffering capacity of the soil and water are likely to return the pH to acceptable levels within a relatively short period.
Sulphuric acid is fast-acting and is quickly neutralised in the environment by reacting with the vegetation canopy (which intercepts much of the chemical), soil and water in the soil. This means that the hazards associated with this chemical rapidly decrease from the time of application.
Sulphuric acid is known to break down relatively quickly, reducing the possibility of problems with long term effects on the environment. In order to gain approval for use as a commodity chemical, information will also have been assessed to confirm that such use does not pose a risk to wildlife. The risks to birds, mammals, various invertebrates and aquatic life would each have been evaluated and any necessary restrictions placed upon the use of the chemical.
Future Changes To The Approval of Sulphuric Acid and other Commodity Chemicals
Sulphuric acid was supported for review in the fourth stage of the European Community (EC) review programme under Directive 91/414/EEC. More details of the Fourth Stage of the Review Programme are on the CRD website.
However, Sulphuric acid was not included on Annex I of 91/414/EEC. The non-inclusion Decision 2008/937/EC (pdf, 2 pages), for sulphuric acid was published on 12 December 2008.
The Commodity Substance Approval for plant protection uses of sulphuric acid must now be revoked to comply with the EC Decision. The Revocation Notice for sulphuric acid can be viewed on the CRD website.
The final date for use of sulphuric acid for plant protection purposes will be 5 June 2010.
Further information on sulphuric acid is available in the Advisory Committee on Pesticides Evaluation Document on the substance (Evaluation on: Sulphuric Acid, April 1998, document no. 174).
Guidance concerning the approval of commodity chemicals, including sulphuric acid as pesticides.
Advisory Committee on Pesticides (ACP).
Commodity Substance Approval for Sulphuric Acid.
Code of Best Practice for the Use of Sulphuric Acid.
Code of Practice for Using Plant Protection Products (replaces "Green Code").
Control of Substances Hazardous to Health (COSHH) Regulations.
National Association of Agricultural Contractors.
N.P.T.C. (formally known as the National Proficiency Tests Council).