CARIBBEAN FOOD CROPS SOCIETY 37 Thirty Seventh Annual Meeting 2001

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CARIBBEAN FOOD CROPS SOCIETY 37 Thirty Seventh Annual Meeting 2001

Trinidad and Tobago Vol. xxxvn Proceedings of the Caribbean Food Crops Society. 37:104-109. 2001

PESTICIDE RESIDUES ON LOCAL FOOD CROPS: REALITIES AND RECOMMENDATIONS

Ivan Chang Yen, Dept. of Chemistry, The University of the West Indies, St. Augustine; Carlyle Kalloo, Environmental Management Authority, Port of Spain, Trinidad; Isaac Bekele, Dept. of Food Production, The University of the West Indies, Si. Augustine; Wade Lee Fook, Ministry of Agriculture, Centeno, Trinidad; Ronald Barrow, CARINET, St. Augustine, Trinidad

ABSTRACT: A recent market basket survey of organophosphate insecticides in Trinidad clearly indicated improper use of this class of insecticides on produce offered for sale to local consumers. In several cases, crops appeared to have been harvested without regard for recommended pre-harvest intervals, as well as being treated shortly before harvest. On many samples, recommended maximum residue levels were exceeded, particularly on celery, on which mixtures of insecticides were frequently and consistently detected. Supervised field trials of five of the most commonly detected organophosphates showed that recommended pre-harvest intervals of each pesticide were often not in accordance with actual field degradation rates. In some cases, residue levels of pesticides declined faster than expected, raising the possibility of re-infestation of crops by pests within the recommended pre-harvest intervals. Our results indicate a pressing need for supervised efficacy and pesticide residue trials, of all pesticides used on food crops under local growing and storage conditions, and offered for sale locally or exported. The recent acceptance of HACCP for food production systems also mandates regular monitoring of edible crops for contaminants, including pesticide residues, to ensure the safety of consumers.

INTRODUCTION

The effective application of pesticides is a necessity in modern crop protection. For many local fanners, it often represents the only means of guaranteeing their harvests and their livelihood. Unfortunately, pesticide overuse often leads to the development of pest resistance, which in turn results in pesticides becoming ineffective at recommended rates of application, or being ineffective altogether. Consequently, increased rates of application may become necessary for pest control, or by the use of other pesticides or control strategies. However, the development of genetically modified pest-resistant crops, which may reduce the use of pesticides, is not without problems, particularly in Europe (1). The application of combinations of pesticides is a well-established practice in pest control, and is commonly done by local farmers (2). In addition, the "more is better" principle is often adopted in application rates, leading to problems of pesticide residues on harvested crops. Such residue problems are exacerbated by praedial larceny of freshly sprayed crops (3), as well as the non-observance of recommended pre-harvest intervals (PHI), following the final pesticide application. However, pre-harvest intervals are often developed under conditions which may differ significantly from local growing conditions and may thus be considered inappropriate by local farmers. Nevertheless, pesticide residues on crops are cause for concern for consumers, and maximum permissible levels in edible crops have been set for each pesticide (4). Not surprisingly, pesticide residues have occasionally been found on crops exported to the US from the Caribbean (5). Once maximum permissible levels are exceeded, such produce is rejected, and enhanced monitoring of subsequent shipments is implemented. In the face of strong competition from other regions, such action may result in permanent loss of markets for local and regional farmers. In this study, a survey of pesticide application practices by local farmers was undertaken to determine pesticide usage patterns, followed by a market-basket study on the levels of organophosphate pesticides on produce offered for sale to consumers. Supervised field trials on selected organophosphate pesticides were carried out, to determine their persistence patterns and PHI under field conditions, as well as to help explain the results of the market basket study. Summary findings are presented and recommendations made, for the benefit of both the farmer and the consumer.

62 MATERIALS AND METHODS

(a) Farmers ' survey

Farmers (N = 69) in north, central and south Trinidad were interviewed, using a questionnaire. Information obtained on pesticide application practices, including the use of mixtures of pesticides, types of pesticides used on various crops, and the observance of recommended pre-harvest intervals were collated. Results of this survey are presented in Tables 1 and 2.

(b) Market basket study

A total of 200 samples representing 17 crops, was purchased in local markets and supermarkets, for analysis of organophosphate pesticide residues, from September 1996 to May 1997. This number was calculated to represent all produce containing pesticide levels above the Codex Alimentarius (4) Maximum Residue Levels (MRL), determined within 0.05 units at the 95% confidence level (6). Codex protocols on minimum sample size and items per sample were closely followed in sample collection. Summary results are shown in Table 3.

Five organophosphate (OP) insecticides were applied individually to Pak Choi Brassisca sinensis L), using a randomized block design and 200 plants per treatment. Eight spray applications were made at recommended rates of application for each pesticide during the dry season. In comparison, five applications were made during the wet season, since applications were made only during periods of little or no rainfall, until close to crop maturation. The method of analysis used (7) was validated prior to sampling, and quality control measures implemented during the entire programme. Calculated values of pr-harvest intervals required for each pesticide to fall below its MRL are summarized in Table 4.

RESULTS AND DISCUSSION

(a) Farmers ' survey

Table 1 shows the summary data on use patterns of pesticides, excluding herbicides, by local farmers. A wide range of different chemical classes are used in crop protection, with the most used pesticides being profenofos, used as two different formulations, and Cypermethrin. In addition, the same formulation of a pesticides could be used on a range of crops to control different pests. For example, for OP pesticides, up to 34 different formulations, containing 27 OP pesticides, were used on tomatoes, while 27 different formulations with 16 OP were used on cabbages (Table 2). Likewise, mixtures of pesticides were applied simultaneously, often using the "more is better" principle. Spreaders and stickers were also used to enhance pesticide persistence, mainly during the wet season, but appear to be increasingly used in the dry season as well. Pesticides were normally applied to cash crops at 4-5 day intervals in the dry season, and even more frequently during the wet season. Recommended pre-harvest intervals were often not strictly adhered to, this practice being encouraged by consumers preferring unblemished produce, as well as incidents of praedial larceny.

63 (b) Market basket study

Of the 200 samples analyzed, 22% contained detectable OP pesticides, of which 10% exceeded Codex Alimentarius MRL (4). The worst affected crop was locally grown celery, with 15 of 18 samples containing detectable OP residues, 13 above the MRL. The most commonly detected OP was methamidophos, followed by triazophos, profenofos, diazinon, ethion, pirimiphos methyl and dimethoate. These results in Table 3 were consistent with our farmers' survey data, with respect to pesticide use patterns and practices, including the observance of pre-harvest intervals. For example, the 40.20mg/kg triazophos and 15.74mg/kg methamidophos levels on celery are well above the MRL and pose a significant threat to the health of the consumer. Similarly, the 8.52mg/kg profenofos level, also on celery, strongly implies that harvesting was carried out soon after spray application, since this pesticide decays rapidly once applied in the field (8). Our market basket data strongly suggest the need for increased monitoring of produce offered for sale to consumers. Continued education of farmers on the observance of safe pre-harvest intervals is also required.

For each pesticide, the residue (Y) at time (t) fitted and exponential decay model of the following form, representing the pesticide decay rate:

Y = a + b e"cl where Y is the fitted pesticide concentration; t is the time (days) after spray application; a, b, and c (c>0) are the estimated parameters; (a + b) denotes the initial pesticide level. The time taken for each pesticide to decay to below the MRL was calculated for both wet and dry seasons. Results are shown in Table 4. Of the five OP pesticides investigated, triazophos was highly persistent in both wet and dry seasons, while methamidiphos was more persistent under dry than wet conditions. In comparison, phenthoate, profenofos and pirimiphos methyl disappeared rapidly under wet or dry conditions. Our pre-harvest intervals, calculated for pesticide levels to fall below the Codex MRL, compared well with those recommended by the pesticide manufacturers for pirimiphos. However, for phenthoate and profenofos, our rates were about half those recommended by the manufacturers; while this provides added safety for the consumer, it could lead to pest re-infestation, if the pesticide levels become too low to maintain control. For methamidophos, the experimental and manufacturer's values agreed for the dry but not the wet season. In comparison, triazophos required about a week more than recommended, to fall below its MRL, and can result in produce being harvested before the MRL is achieved. These findings may explain the detection of methamidophos and triazophos on several samples of our market basket survey.

CONCLUSIONS AND RECOMMENDATIONS

The results of our studies clearly illustrate the realities that must be faced, if the many problems facing the farmer and the consumer are to resolved. Obviously much more needs to be done to maximize the benefits of pesticide applications, as well as to protect the health of consumers. Since our studies involved only OP pesticides, the other classes of pesticides, particularly the carbamates, many of which are even more toxic to humans than the OP (Table 1), require similar attention. Efficacy trials are urgently required, to optimize the effectiveness of pesticide applications, using multidisciplinary teams of pesticide application and residue scientists, entomologists, plant

64 geneticists and statisticians. Such trials can allow pre-harvest intervals following final pesticide applications, appropriate to local growing conditions, to be developed with the required degree of confidence. The identification of less persistent but effective pesticides closer to harvest can also result from such studies, for the benefit of both farmer and the consumer. Since effective implementation of HACCP systems is likely to become a requirement for the continued export of fresh produce to other countries, regular monitoring of pesticide residues should be carried out, as evidence of such implementation. To this end, revised legislation to control the quality of local foods with respect to pesticide residues has already been implemented (9) and should be used to good effect.

ACKNOWLEDGEMENTS

The authors are grateful to the Ministries and Agriculture and Health for the provision of facilities and technical assistance for this project, and to the University of the West Indies for financial support.

REFERENCES

1. Thayer A.M. (1999) AG Biotech food: Risky or risk-free? Chemical and Engineering News November 1, 11-20. 2. Chang Yen L, Bekele I., Kalloo C. (1999) Use patterns and residual levels of organophosphate pesticides on vegetables in Trinidad, West Indies. J. AOAC International 82, 991-95. 3. Daily Express Trinidad (1998). Beware Poisoned Seasoning. June 27:6. 4. Codex Alimentarius (1993) Vol.2. Pesticide Residues in food. Joint FAO/WHO Food Standards Programme, Codex Alimentarius Commission. 475pp. 5. US Food and Drug Administration Center for Food Safety and Applied Nutrition Pesticide Program: Residue monitoring 1995. Internet add. http://vm.cfsan.fda.gov/~dms/pes95res.html 6. Larsen R.J. and Marx M.L. (1986) in An Introduction to Mathematical Statistics and Its Applications. Second edit. Prentice-Hall, Englewood Cliffs, N.J. 280-281. 7. Luke, M., Froberg, J., Doose, M. & Masumoto, H. (1981) J. Assoc. Off. Anal. Chem. 64, 1187-1195. 8. Pesticide Residues in Food (1992). Evaluations 1992, Part I-Residues. Food and Agricultural Organization of the United Nations, 118, 769-782. (9) The Pesticide and Toxic Chemicals Act (1979) Republic of Trinidad and Tobago: An act to regulate the importation, storage, manufacture, sale, use and transportation of pesticides and toxic chemicals and to provide for the establishment of the Pesticides and Toxic Chemicals Board. 21pp.

65 Table 1. Farmers' Survey on Use of Pesticic es in Trinidad. Frequency of Use Chemical name (%) Type / LD 50(mg/kg) Function Profenofos 15.68 Organophosphate / 358 Insecticide Cypermethrin 15.52 Pyrcthroid / >4920 Insecticide Copper salts 11.11 Copper/> 2000 Fungicide Mancozeb 9.64 Dithiocarbamatc / >5000 Fungicide Chlorothalonil 6.05 Chlorothalonitril / >10000 Fungicide Methamidophos 5.72 Organophosphate / 20 Insecticide Oxamyl 5.07 Carbamate / 5.4 Insecticide/Acaricide Cartap 4.74 Thiocarbamate / 335 Insecticide Bacillus thuringiensis 4.58 Biological / ND Insecticide Phenthoate 2.61 Organophosphate / 410 Insecticide/Acaricide Triazophos 2.45 Organophosphate / 58 Insecticide Benomyl 1.96 Carbamate / >5000 Fungicide Methomyl 1.8 Carbamate / 20 Insecticide/Acaricide Teflubenzuron 1.63 Substituted urea / >5000 Insect growth regulator Pirimiphos methyl 1.63 Organophosphate / 2050 Insecticide/Acaricide Fenbutatin oxide 1.47 Organotin / 2631 Acaricide Formetanate 1.31 Carbamate / 20 Insecticide/Acaricide Fenvalerate 1.31 Pyrethroid / 451 Insecticide/Acaricide Ethion 1.14 Organophosphate / 208 Insecticide/Acaricide Dicofol 1.14 Chlorinated alcohol / 578 Acaricide Malathion 0.98 Organophosphate / 2000 Insecticide Dimethoate 0.82 Organophosphate / 387 Insecticide Diazinon 0.82 Organophosphate / 1250 Insecticide Carbosulfan 0.82 Carbamate / 250 Insecticide

Table 2. Use of Organophosphate Pesticides on Selected Produce in Trinidad. Crop No. of different formulations used No. of active ingredients in formulations Tomato 34 27 Cabbage 27 16 Eggplant 22 20 Cauliflower 16 13 Sweet pepper 23 19 Okra 16 16 Cucumber 13 14

66 Table 3. The time taken for each pesticide to decay to below the MRL calculated for both wet and dry seasons. No. No. Exceeding Organophosphates, Organophosphates positive MRL Exceeding MRL Not Exceeding MRL 1 0 none Ethion, dimethoate 1 0 none Ethion, pirimiphos 15 13 Diazinon, profenofos, pirimiphos, Malathion, pirimiphos, methamidophos, triazophos diazinon, methamidophos 4 1 Triazophos, methamidophos Profenofos, pirimiphos 6 0 none Methamidophos 5 2 Triazophos, ethion Profenofos, triazophos, ethion, dimethoate 1 0 none Diazinon 6 3 Methamidophos Diazinon, methamidophos 0 0 none none 1 0 none Diazinon 0 0 none none 3 1 Methamidophos Diazinon 0 0 none none 0 0 none none 0 0 none none 1 0 none Ethion 0 0 none none 44 20

Table 3. Calculated Pre-Harvest Intervals from Field Trials Compared to Manufacturers' Recommended Values. Pesticide Season Calculated PHI (days) Manufacturers' PHI (days) Pirimiphos Dry <1 3-7 Wet 2 Phenthoate Dry 3 14-21 Wet 2 Profenofos Dry >7 15 Wet 6 Triazophos Dry 28 21 Wet >21 Methamidophos Dry >14 14-21 Wet 6