Swiss Info has conducted a very interesting investigation into a category of pesticides (plant protection products) – growth regulators, or ‘growth hormones’ – which are administered to plants, including non-organic cereals and fruit. (1)
1) Growth hormones in apples, why?
The annual consumption of growth regulators in Switzerland is equivalent to that needed to spray 83% of the entire surface area used for growing apples. Growth regulators, also known as ‘cosmetic pesticides’, are used for two purposes:
– improve the appearance (size and color) of the fruit, to ensure its best classification and thus the best selling price;
-chemical thinning. To make the ‘excess’ fruits fall and allow the remaining ones to grow larger, without having to resort to manual or mechanical selection.
2) Zurich Polytechnic, the investigation on apple orchards
The Swiss Federal Institute of Technology in Zurich conducted a survey of nearly 200 producing companies, representing a quarter of the Swiss surface area used for apple cultivation. Researcher Lucca Zachmann, interviewed by Swiss Info, reported that:
-59.2% of the farmers interviewed declared that they use growth hormones (phytoregulators) for chemical thinning
-23.5% instead declared that they use plant growth regulators mainly to improve the appearance of apples.
The use of plant growth regulators is more widespread among farmers who distribute apples through commercial channels than among those who sell directly. In fact, ‘Class 2’ apples are paid 59% less than ‘Class 1’ apples by intermediaries, and only 33% less by consumers.
3) Plant growth regulators, possible risks for human health
A recent scientific review from Peking University (Xiaoxia et al., 2023) on the toxicity of ‘plant hormones’ (Plant Growth Regulators, PGRs) to humans and animals reports the following:
–‘Plant growth regulators are one of the most widely used categories of pesticides today, also because they are considered relatively low in toxicity compared to other pesticides. However, their widespread use can lead to overexposure from multiple sources;
-exposure to ‘plant hormones’ is associated with various toxicities affecting many organs of our body, such as toxicity to the testes, ovaries, liver, kidneys and brain. In addition, some PGRs are considered potential endocrine disruptors’. (2)
3.1) Reproductive and developmental toxicity
The FiBL scientific review from Peking University also highlights that ‘there is evidence of developmental and reproductive toxicity associated with prenatal and postnatal exposure in both animals and humans.
PGRs can influence the synthesis and secretion of sex hormones, destroy the structure and function of the reproductive system, and impair the growth and development of offspring (…).
The management of comprehensive epidemiological studies will be essential to assess the reproductive and developmental toxicity resulting from a mixture of various PGRs, with particular attention to understanding the underlying molecular mechanisms’. (2)
4) Exposure of humans to plant hormones, the US study
A research conducted by the Environmental Working Group of Washington (Temkin et al., 2024) has also investigated the levels of exposure of the adult population, in three US states, to chlormequat. One of the most used ‘plant hormones’ in cereal crops in North America.
‘Toxicological studies suggest that exposure to chlormequat may impair fertility and harm the developing fetus at doses lower than those used by regulatory agencies to establish permissible daily intake levels.’
The detection of chlormequat in urine samples from adults collected in South Carolina, Missouri and Florida has progressively increased over the three periods in which the analyses were conducted (2017, 2018-2022, 2023). From 69% of samples to 74%, up to 90%. (3)
5) Not just fruit and vegetables. Non-organic cereals also at risk
US researchers observed a high prevalence of chlormequat in oat and wheat-based foods:
-92% (23 out of 25) of non-organic products purchased in the US in 2022-2023 showed detectable levels of chlormequat, in concentrations up to 291 µg/kg (114 µg/kg average in 2023);
-22% (2 out of 9) of the few wheat-based products analyzed instead detected low concentrations of chlormequat, from 3.5 to 12.6 µg/kg.
‘These findings and the toxicity data from chlormequat raise concerns about current exposure levels and warrant more extensive toxicity testing, food monitoring and epidemiological studies to assess the health effects of chlormequat exposure in humans.’ (3)
6) Plant growth regulators authorised in the EU and Switzerland
Growth hormones for plants, or phytoregulators, are classified as pesticides (Plant-Protection Products) and therefore subject to the relevant regulations, with regard to the (still opaque. See note 4) authorisation procedure, labelling requirements and maximum residue levels in food.
Switzerland still authorizes the use of four of the eight ‘growth hormones’ for plants identified by WHO as ‘moderately hazardous’:
-chlormequat cited in the US study mentioned above (3)
-naphthyloxyacetic acid
-paclobutrazol
-mepiquat.
In the European Union, however, the use of the last two phytogrowth regulators mentioned is authorised. EFSA has also just published a ‘peer-review’ on BASF’s request for the renewal of the authorisation of mepiquat. (5)
7) Provisional conclusions
The uses of ‘growth hormones’ in plants are manifold, extending to grapes and other fruits, among others.
Organic products remain the only shelter from dietary exposure to these substances.
On hold for further studies and new commitments to free agriculture from toxic chemicals.
Dario Dongo
Footnotes
(1) Nerys Avery. What is the price of the perfect apple? Swissinfo.ch. 10.14.24 https://tinyurl.com/yh2tjs5b
(2) Xiaoxia Wang, Weidong Hao. Reproductive and developmental toxicity of plant growth regulators in humans and animals. Pesticide Biochemistry and Physiology, Volume 196, 2023, 105640. https://doi.org/10.1016/j.pestbp.2023.105640
(3) Temkin, A.M., Evans, S., Spyropoulos, D.D. et al. A pilot study of chlormequat in food and urine from adults in the United States from 2017 to 2023. J Expo Sci Environ Epidemiol 34, 317–321 (2024). https://doi.org/10.1038/s41370-024-00643-4
(4) Marta Strinati. EU, opaqueness of decisions on pesticides. Pollinis’ petition. GIFT (Great Italian Food Trade). 22.10.24
(5) EFSA (2024). Peer review of the pesticide risk assessment of the active substance mepiquat (evaluated variant mepiquat chloride). https://doi.org/10.2903/j.efsa.2024.8923
Dario Dongo, lawyer and journalist, PhD in international food law, founder of WIISE (FARE - GIFT - Food Times) and Égalité.
