Modelling human pesticide kinetics based on oral and dermal exposure data derived in a controlled setting

The current research contributes to the Sustainable Plant Protection Transition
(SPRINT) Project (see https://sprint-h2020.eu/) in the EU Horizon Programme and
is part of a work package on Exposure Assessment. Plant protection products
(PPP, in this protocol referred to as *pesticides*) are primarily taken up as
residues from the diet. In addition, there is a contribution from so-called
non-dietary sources which may vary in the general population, depending on
sub-group (e.g. applicators such as farmers or *neighbours* who live close to
agricultural land). Dietary exposure is by ingestion and non-dietary exposure
may be related to inhalation (e.g. spray drift) or dermal absorption (direct
skin contact) at relatively high levels during application or at much lower
levels in a home next to an agricultural field where pesticides are applied
(so-called bystander exposure).

In the SPRINT project we study exposure in three subgroups from the general
population: farmers, neighbours and consumers. The main study method will be by
human biological monitoring (HBM). For interpretation of the HBM results
understanding the kinetic process of uptake, distribution, metabolism and
excretion (ADME) is vital. In the current protocol we propose to do a study at
low dose in human volunteers to describe these kinetic parameters that will
later be used for physiology-based biokinetic (PBK) modelling to support
interpretation of the HBM findings and calculate the dose in target tissues.

The collection of HBM data in the population-based observational study
(HBM-survey) was already completed according to an approved study protocol
registered under dossier number: 2020-7248 and NL-number: NL76296.091.20 (1).
Based on this study outcome we were able to pre-select pesticides for the
current human volunteer study according to occurrence and hazard, using the
hazard quotient (HQ) approach to identify the highest priority pesticides by
ranking from high to low HQ (2).

Humans are exposed to pesticides through several routes. In the general
population, pesticide residues on food cause dietary intake of pesticides. In
addition, non-dietary exposure occurs through household use of pesticides, e.g.
use of insecticide sprays indoors in or around a private home, potentially
leading to inhalation or dermal absorption. In addition, farmers are exposed in
an occupational setting during application of pesticides to crops. This
multi-route exposure, combined with a lack of knowledge on toxicokinetics,
makes it difficult to estimate whether the ADI for pesticides is exceeded.
Improved understanding of pesticide kinetics will aid in the determination of
human exposure in the general population.

Understanding human pesticide kinetics is crucial for transitioning towards
more sustainable plant protection. The EU has established the Farm-to-Fork
strategy within the European Green Deal, aiming to make food systems fair,
healthy and environmentally friendly. The Commission aims at achieving a 50%
reduction in the overall use and risk of chemical pesticides in 2030. Increased
understanding of human kinetics will aid in the transitioning towards safer
harvest protection.
According to EU regulations the pre-market evaluation of a new PPP does not
require a human volunteer study aimed at characterisation of the kinetics of
uptake, distribution, metabolism and excretion in humans. For the proposed
pesticides there is currently not sufficient knowledge on kinetics in humans to
be able to interpret the results of our HBM survey with respect to the
toxicokinetics.

Several similar human toxicokinetic models already exist for pesticides, such
as that of Auton et al. for dermal exposure or Oerlemans et al. for
tebuconazole(3, 4). However, using human kinetic data to create a PBK model to
predict intake of specific pesticides is not yet available for most pesticides.
In addition, the development of a generic human PBK model for pesticides
requires empirical data on multiple pesticides to verify that the PBK model
works for a broad chemical spectrum.

The study will add new information on the kinetics of selected pesticides after
oral and dermal exposure, and to what extent differences between and within
males and females can be expected. For several pesticides some toxicokinetic
data has been published based on human (volunteer) studies. This is summarized
in section 6.3. This information will help to aid the understanding pesticide
kinetics, and contribute to the development of computational models to predict
oral or dermal exposure to pesticides in the general population.

Primary Objective:
To collect human data of the kinetics of pesticides after a single oral or
dermal dose to create a physiology-base pharmacokinetic (PBK) model.

Secondary Objective(s):
The models that will be parameterised with these data will also be used to:
a. perform calculations of the dose of the parent and its metabolites in
internal organs for follow-up testing of specific organ toxicity;
b. perform back-calculations (reverse-dosimetry) related exposure scenarios
observed in real life to evaluate how HBM findings are related to currently
established safe values.

The design is a laboratory-based controlled kinetic study. Study subjects (see
section 4) will be their own reference as we will start to collect samples of
body fluids before the pesticide of interest will be administered. All study
participants will receive the same dose and samples of body fluids will be
collected over time. A similar study design has been used in our research group
by Oerlemans et al. to study kinetics of tebuconazole in healthy volunteers (3).

Study participants will be asked to participate in two single exposure
scenarios (oral and skin absorption) separated by a wash-out period of at least
one week to avoid carry-over.
Exposure at baseline will be verified before the administration of the
pesticide of interest. Study subjects will be advised to avoid foods and
beverages known to contain high residue levels of the pesticide of interest,
and document this prior to their visit. During the visit the research
department food and beverages will be provided.

The dose will not exceed the ADI for that pesticide. One session will be
dedicated to oral administration and the other session involves dermal exposure
of the substance of interest dissolved in a volatile organic solvent (ethanol)
that will evaporate, leaving a known topical dose on the skin surface. For
reasons of comparison, each volunteer will be exposed to the same substance
orally and dermally.

Oral exposure to a pesticide
Dermal exposure to a pesticide

Participants will not experience any benefits from taking the investigational
product used in this study.

The potential risks of short-term exposure have been summarized in the
International Chemical Safety Cards (ICSCs) for the following pesticides:
ICSC 0859 - LAMBDA-CYHALOTHRIN (ilo.org)
ICSC 0246 - CYPERMETHRIN (ilo.org)
ICSC 0247 - DELTAMETHRIN (ilo.org)
ICSC 0160 - GLYPHOSATE (ilo.org)
ICSC 1347 - PIPERONYL BUTOXIDE (ilo.org)
ICSC 1303 - IMAZALIL (ilo.org)
ICSC 0033 - 2,4-D (ilo.org)

The risks of other pesticides have been summarized by Haz-Map:
Tebuconazole - Hazardous Agents | Haz-Map
Acetamiprid - Hazardous Agents | Haz-Map
Cyprodinil - Hazardous Agents | Haz-Map
Bromoxynil - Hazardous Agents | Haz-Map

Risks of fluopyram exposure has been summarized by the Ctgb (the Netherlands):
Fluopyram: Ctgb Toelating: Luna Sensation

Information on the hazard of fluazifop-P can be found on the manufacturers
label: 00394108-001-002.pdf (nufarm.com)

(see also: pg. 26 and 27 in the study protocol