How robust is our pesticide policy? A case of waiting period or post-harvest interval for safe consumption of produce

Top: Saurashtra farmer who was keen to offer us a gift of maize, but for spray a day before; Bottom: Ready to spray with mixture on cotton.

 

As early as 1985, India recognised importance of integrated pest management to achieving optimal crop protection in its agricultural policy. This policy also envisaged reduction in the use of synthetic pesticides and increase in eco-friendly safe tactics in the agroecosystem. Safety to all is pivotal of crop protection policy. However, synthetic pesticides remained the bulwark of integrated pest management in agriculture. In fact, consumption of synthetic pesticides has increased over the past two decades from about 45,000 tons to about 60,000 tons. And hence, it has become necessary that we use pesticides judiciously so that farmers save their farm produce from the ravages of pests and at the same time, consumers get foodgrains and other farm produce that are safe to eat.

Some years back, I was reading the data on major uses of pesticides, especially related to post-harvest interval [PHI] or waiting period for harvesting the produce after pesticidal spray so that no amount of pesticide is found above the maximum residual limit [MRL] for the safe consumption by humans. I felt some discrepancies. Before coming to these discrepancies, let me explain to you as to how the waiting period is calculated for the human safety.

For the registration of pesticide, it has to be effective against the target pests in a crop and also safe to the human and environment. Once, the field dose is fixed after three locations two season bioefficacy trials, the next step is fixation of MRL in the produce as per Food Safety and Standards Authority of India [FSSAI] guidelines under the Ministry of Health and Family Welfare, Government of India’s Food Safety and Standards Act [FSSA] 2006. Crop is raised as per good agricultural practice and sprayed as recommended with pesticide at approved field application dose as well as at 25% higher-than-the recommended dose [as per FSSAI Guidance Document-SOP MRL 16.03.2022] during flowering or grain formation stage. This is repeated at four locations in two seasons, total of 8 locations which is minimum need, but could exceed in case of major crop. These pesticide residue data on the tentative day after application [varies depending upon the crop] are then fed to excel-based OECD MRL calculator to get MRL. This estimate is based upon the mean of residues+4-times standard deviation [SD] which may be many-fold higher than the lowest residue value of one of the samples. With MRL, acceptable daily intake [ADI mg/kg bw/day] and notional consumption of the produce of that crop [kg/day/person], the national estimated daily intake [NEDI] is calculated using human average body weight of 60 kg. If NEDI is substantially less of ADI, then MRL is accepted. Most countries follow their own standard operating procedures harmonised on the guidelines of OECD-FAO. Many developed countries ensure stringent MRL levels so that foodstuffs imported or produced in their countries do not contain pesticide residue of any concern to the safety of humans and animals.  In India, the FSSAI undertakes responsibility of fixing MRLs of pesticides in different crops under the FSSA 2006 and notifies them regularly. After MRL in a produce is fixed, the next step is to estimate half-life of pesticide and then PHI or waiting period under the prevailing crop conditions. The pesticide residues in the produce are also monitored at different time interval until the estimate is equal to or below the limit of quantification [LoQ] of the methodology adopted. There is negative relationship between pesticide residue and time of sampling after pesticide application, which is statistically analysed using log concentration of pesticide residue versus time [days]. This relationship normally follows first-order kinetics and is used for estimating half-life and waiting period until pesticide residue degrades to MRL. The waiting period ensures that produce does not contain pesticide residues above MRL and is safe for human consumption. The Central Insecticide Board and Registration Committee of the Directorate of Plant Protection, Quarantine and Storage at Faridabad [Ministry of Agriculture and Farmers’ Welfare] under the Insecticide Act 1968 mentions waiting period along with field application rates [g ai/ha for technical, kg/ha for formulation and lt/ha for final spray solution].

The waiting period however depends upon environmental factors, genetic traits of crops as well as agronomic practices. Over the years, agronomic practices including crop protection practices have undergone a sea change. For e.g., protective farming practices like poly-houses, nethouses have increased pesticidal stability and hence, affected adversely waiting period. Drone applications may also similarly affect waiting period as pesticide is applied in much concentrated form than the diluted solution in high volume as much as 500 lt/ha, and likely to stay on crop more than drip-off of high volume sprays. Hence, waiting periods of various pesticides should clearly be specified along with the agronomic conditions under which these are prescribed. Considering the diversity of agro-climatic conditions, the MRL which is based upon the sum of mean + 4-time SD is more sensitive to the health needs of vulnerable food-insecure section of population.

Coming to waiting periods, here are some anomalies that I observed during limited study. For e.g., Dicofol 18.5% EC formulation meant for mite control is found to have the same waiting period of 15-20 days on crops as diverse as tea, citrus, litchi, okra and cotton, for the field dose [g ai/ha] ranging from 230 [for tea] to 500-1000 [for rest four crops]. And this recommendation holds good and did not change from 2012 to 2023 on the basis of documents entitled “Major uses of pesticides [MUP]” under the Insecticide Act 1968 updated from 2012 until 1^st Feb, 2023, respectively. It seems illogical for waiting period to be the same as physiology of these crops differ a lot and so also their ability to dissipate and metabolise dicofol.

Another case is of imidacloprid pertaining to non-edible crop like cotton where waiting period appears to be a contentious issue depending upon the formulations. As per the above document updated to 1^st Feb., 2023; waiting periods are not required [abbreviated as NR] for its formulations like 48% FS and 70% WS, but these are mentioned for other formulations like imidacloprid 70% WG [7 days], imidacloprid 17.1% SL [50 days], imidacloprid 17.8% SL [40 days] and imidacloprid 30.5% SC [26 days]. All formulations are meant for control of sucking pests like aphids, whitefly, jassids and thrips. Those formulations where waiting periods are mentioned, are recommended at the field dose ranging from 20 to 50 g ai/ha while those formulations where waiting period is not mentioned [required], are recommended at the much higher field dose ranging from 300 to 700 g ai/ha. It seems odd that the higher doses are excluded from the estimation of waiting periods. Are the waiting periods relevant for the non-edible crop like cotton? It is another matter that cotton seed is used for edible oil consumption and may need to be regulated in terms of safety for the presence of pesticide contamination.

Take another case where higher dose does not make difference to waiting period, rather lowers the waiting period. Diafenthiuron 50% WP applied at the dose of 300 g ai/ha has a waiting period of 21 days on cotton while the same insecticide applied at the lower dose of 239 g ai/ha has a longer waiting period of 30 days as per recommendation given on the 1^st Feb 2023. Isn’t dose dependency a factor in waiting period estimation? CIBRC’s recommendations obviously contradicts the report that MRL is positively impacted by the application dose as outlined in this OECD document [https://one.oecd.org/document/ENV/JM/MONO(2011)50/REV1/ANN/en/pdf].

Chlorantraniliprole is an important insecticide used for lepidopteran control. Formulation alone should not make significant difference to waiting period, if the dose per ha is the same. However, Chlorantraniliprole 18.5% SC at 75 g ai/ha for the control of early shoot borer of sugarcane has a waiting period of 208 days while Chlorantraniliprole 0.40 GR at the same dose for the control of early shoot borer has a waiting period of 147 days. It is quite intriguing that a significant difference in waiting period is attributed to the formulation alone. Furthermore, top shoot borer infests from the 6^nd month onward causing side branching, and assuming that in the state like UP where annual crop of sugarcane is taken, harvesting of annual crop will not concur with the 208-day waiting period recommended for 18.5% SC formulation.

Similarly, chlorantraniliprole 18.5% SC formulation has a waiting period of 22 days in brinjal and similar for urd, soybean, tur and black gram, as compared to much lower waiting periods in some vegetable crops like cabbage [3 days], tomato [3], chilli [3], okra [5] and bitter gourd [7]. In case of brinjal, longer waiting period of 22 days will affect the harvesting of fruits that is normally done within a week. There are many similar examples in the MUP document updated periodically.

Flubendamide is used for the lepidopteran control. Flubendamide at the rate of 48 g ai/ha [appears to erroneously at 100 g/ha for both formulations 20% WG and 39.35% SC] is reported to have waiting period of 5 days on tomato assumed to be under the open field conditions based upon the MRL of 2 mg/kg [FSSAI in its version v19.08.20 and MUP as early as 2012]. Tomatoes are being grown these days in polyhouse conditions. As per Singh et al. [2023], longer waiting period is advisable for tomato grown under polyhouse conditions than those grown under open field conditions. This seems logical as pesticide degradation is slower under the protection conditions. Review of literature on the half-life, closely related to waiting period, showed that half-life of flubendamide on tomato varies a lot, 2.25 days [Singh et al., 2023], 6.07 days [Kelageri et al. 2017], 0.33-3.28 days [Sharma et al. 2014] and 1.64 days [Paramsivam and Banerjee, 2012]. Whereas these publications give details of procedures and are subjected to critical review, the field reports related to dissipation of flubendamide on tomato of the pesticide company on which CIBRC recommendations are based, were not available for critical review at the time of registration under the disguise of confidentiality, nor are they available many years after registration. It is therefore a matter as what to believe in.

Considering the above points, it is necessary that regulatory agencies specify the conditions where the existing MRLs as well as waiting periods or PHI are validated and also ensure that these are commensurate with the current agronomic practices.

Kelageri S S et al. 2017. Int J Agri Env Biotech 10(6), 651-67.

Paramsivam M and Banerjee H 2012. Bull Environ Contam Toxicol 88(3), 344-8.

Singh S et al. 2023.Heliyon 9 e 14963.

Sharma K K et al. 2014. Bull Environ Contam Toxicol 86(11),7673-82.