Half-Lives of Pesticides on Greenhouse Crops

Abstract

Re-entry exposure to pesticide residues have been reported to result in potential health risk . For risk assessment purposes it is therefore essential to characterize the exposure processes. Since especially dermal exposure is important in this context, this requires special attention.Models for re-entry exposure estimates have been developed over the past 10 years Leffingwell 1982. Nigg et al. 1984;Zweig et al. 1985). Recent reviews have considered these issues for greenhouse crops in more detail (Van Hemmen, 1993, Van Hemmen et al., 1995. The basic assumption of the developed models is that exposure results from the transfer of pesticide residue present at the crop during worker activities. More specifically, it was stated that dermal exposure (DE [g/day]) is determined by the amount of transferable residue (expressed as dislodgeable foliar residue DFR [g/m 2 ], a crop and work activity specific-transfer factor (TF [m 2 /hr) and duration of re-entry (T, [hr/day]), which can be expressed in the most genera1 form as:where: DE i = DFR i,t * i = i-th pesticide m = m-th task t = t-th day after application.The transfer factor (TF) is an empirical factor which is assumed to be crop and activity specific but pesticide independent. TF's have been derived from exposure data and data on dislodgeable foliar residue established for a variety of crop activities, and are accepted to be relevant for risk assessment. However, within crop and activities variances of the TF may be substantial (Krieger et al. 1991).The actual dislodgeable foliar residue at time of re-entry is considered to be an important source strength for dermal exposure. The level of actual pesticide residue may differ from the initial amount of DFR depending on the decay rate and the elapsed time since application. The dissipation of the foliar pesticide deposit is considered to be a complex process of environmental factors, metabolism and translocation (foliar penetration and plant growth), and pesticide formulation (Bentson 1990). Willis and McDowell (1987) assumed that the process of decay may in many cases be described by a first order process. Thus, the relationship between initial and actual DFR can be described as:

Development of a Data Set of Pesticide Dissipation Rates in/on Various Plant Matrices for the Pesticide Properties Database (PPDB)

“…Dissipation rates also have value when considering the potential risk to non-target and beneficial organisms (e.g., pollinators) that may forage or otherwise come in contact with a pesticide treated plant, as well as informing on how long the chemical is likely to offer satisfactory pest control before it decays [6][7][8]. As a consequence, plant matrix half-lives are often an important input parameter into various risk assessment models [9][10][11][12].In this context, dissipation rate is defined as the rate at which the pesticide active substance disappears from the part of the plant measured due to the combined effects of different processes Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: …”

Degradation of Propamocarb-hydrochloride in Tomatoes, Potatoes and Cucumber Using HPLC–DAD and QuEChERS Methodology

“…Also Omirou reported that the highest residue levels in both treatments were determined in samples taken in the first sampling just after pesticide application as in our case. In another study by Beouwer was reported that the dissipation of pesticide deposit was a complex process depingding on various environmental factors like temperature, relative humidity and UV irradiation), metabolism and translocation (pesticide penetration and plant growth), application technique and pesticide formulation (Brouwer et al 1997;Katagi 2004;McCrady and Maggard 1993). Nd not detectable a n = 3…”

Determination of Bromothalonil Residues and Degradation in Apple and Soil by QuEChERS and GC–MS/MS

“…It was readily debrominated and degraded into 2-methyleneglutaronitrile Sauer et al 1998). Many factors such as the local soil characteristics and climate might affect the dissipation of bromothalonil (Brouwer et al 1997;Katagi 2004). The dissipation of bromothalonil in apple was faster than in soil under field conditions.…”