New tests reveal high residues

Research findings announced by the Ministry of Agriculture (MA FF) on 18 January have shown that unexpectedly high residues of organophosphate (OP) insecticides occur in some carrots(1)’. The Ministry has announced restrictions on the use of OPs to restore the margins of safety.

Residues found in carrots

A change of sampling technique in which carrots were analysed on an individual root basis has shown that 1-2% of carrots contain OP residues up to 25 times higher than expected. Past monitoring had been based on the analysis of composite samples of carrots in accordance with internationally recognised methods of sampling.

Residue levels of tested carrots varied by large factors, from below the level of detection to in excess of the maximum residue limit (MRL). A summary of residues detected in individual carrot roots is given in Table 1. These results have been collated by the Working Party on Pesticides Residues (WPPR), which reports to the Advisory Committee on Pesticides (ACP). Carrots from commercial sources were generally found to comply with MRLs. However, recent samples, which showed high variability on the individual carrot analysis, were taken from the same bulk sample.

The root of the problem

OPs are mainly used on carrots to control the carrot root fly Psila rosae. In the UK, the OPs chlorfenvinphos, phorate, triazophos, quinalphos and primiphos-methyl have been widely used over the last 25 years to control the season’s first and possibly second generation larvae which attack the root. In the mid-1960s carrots received an average of two applications per season (one an OP and one an organochlorine). Since then there has been a progressive increase in the area of carrots

treated with OPs. In 1966. a total of 3.000 hectares were treated with one or two pesticides while by 1991. virtually the entire crop was treated with up to seven different OPs

Residues persist

Ministry officials are at a loss to explain how these high levels have occurred. Sampling under the current internationally recognised protocol does not indicate such hot spot results or misuse by the applicator.

Topping, cutting the top 2-3 mm. and peeling of carrots removes about 4/5 of residues chlorfenvinphos. primiphos-methyl, quinalphos and triazophos. However. data on phorate residues after topping and peeling are not known. This is a problem because phorate is a systemic OP which means that residues can be found throughout the root.

Risk to consumers

The ACP, which advises government ministers, considers that ‘margins of safety have been eroded to a level where action is required to restore them.’ Risk to consumers from pesticide residues are normally assessed in terms of Acceptable Daily Intake (ADI). This means the intake to which a person can be exposed every day throughout life without harm.

OP insecticides however have relatively high acute toxicity which may cause immediate adverse effects after exposure. The highest residues have resulted in the ADI acute being exceeded by up to three times in about half the carrots tested.

MAFF recommendations

In spite of this the ACP considers that there is no immediate threat to human health, they nevertheless make a number of recommendations for urgent consideration. WPPR should carry out further analyses to extend the current available database to confirm the frequency with which high residues of OPs occur in individual carrots. There should be early discussions with the agrochemical manufacturers, carrot growers and retail/consumer interests to explain the findings. (This has been carried out.) All information on resistant varieties, crop covers and cold storage of carrots should be collated in order to consider cultural methods of pest control. The number of OP applications per year should be amended to a maximum of three down from a possible maximum of nine. The possible use of alternative carbamate pesticides (carbofuran and carbosulfan) are suggested.

Angela Browning. the Agriculture Minister accepted all the recommendation of the Advisory Committee on Pesticides.

The Pesticides Trust’s [now PAN UK] response

The unexpected residue results raise a number of issues which require urgent attention:

• It is not clear whether the recently recommended three applications of OPs per year would also produce individual carrots with occasionally high residue levels. OP pesticides can cause adverse neurological effects in both the long and short term. Their use must be urgently reduced to protect those who work with pesticides, as well as consumers. Levels of the carbamate residues carbosulfan and carbofuran in carrots remain uncertain. Is chemical pest control for carrots currently sustainable?

• Research into non-chemical pest control for carrots should be stepped up. These could include the use of resistant varieties, rotation, crop covers, and a change in harvesting strategy. A MAFF 'IPM committee’ should be established which allow such recommendations to be carried out.

• What is the effect in terms of all raw produce? It is not clear if these residue discrepancies are restricted to carrots. The Pesticides Trust therefore calls for the sampling techniques for all produce and pesticide groups to be re-assessed on an individual basis.

• Pesticide reduction policies should be actively considered in all produce sectors. (DB)

References

1. Consumer risk assessment of insecticide residues in carrots. Pesticides Safety Directorate, York, UK.

[This article first appeared in Pesticides News No.27, March 1995, page 3]