Pesticide risk assessment: European framework shows need for safer alternatives

Here, Alberto Mantovani discusses how to balance chemical pesticides with crop-protection and food security, referring to the ever-evolving European framework

Is it possible to protect crops, to ensure food security and, in the meanwhile, to get rid of chemical pesticides at least in the medium-term?

To date, nobody can provide an evidence-based answer. But one aspect is sure: a growing number of widely used pesticides will be drastically limited or banned in the European Union (EU), due to the still-developing regulations and criteria for risk assessment. For example: on August 2019 the European Food Safety Authority (EFSA) published the assessment of chlorpyrifos, a major representative of the organophosphorus insecticides; EFSA concluded that the current approval criteria are not met, because of evident developmental toxicity in laboratory animals and still unclear genotoxic potential.

Thus, a widely used substance will likely need replacement very soon, and similar problems may be predicted for other organophosphates as well: strangely, this big new does not stir much attention by the public and the media.

Leaving aside the complex issue of environmental effects, the ongoing developments on pesticide risk assessment for human health involve both the hazards and the exposure.
The first and main development is the identification of endocrine-disrupting chemicals, so to implement (finally) the Regulation (EC) No 1107/2009: “An active substance […] shall only be approved, if […] not considered to have endocrine-disrupting effects that may cause adverse effects”.

Interestingly the implementation requires a weight-of-evidence approach by the regulatory agencies, as no single test can identify an endocrine disruptor: potentially relevant adverse effects have to be pointed out within the substance’s toxicity profile, and a biologically plausible and robust link with endocrine activity should be established. A significant impact is likely since there are a number of well-established substances ready to be identified as endocrine disruptors, including members of the ethylene bisdithiocarbamate (inhibitors of
thyroid function) and of the conazole (inhibitors of steroid synthesis) groups.

What about developmental neurotoxicity?

Developmental neurotoxicity is another main issue, especially for insecticides; however, till now it has not consistently tackled in the EU. On 2018 EFSA initiated a project to develop an in vitro testing battery for developmental neurotoxicity, exploring the key neurodevelopment processes; the roadmap foresees an EFSA opinion on integrated in vitro/in vivo testing by 2020, paving the way to a specific guidance, possibly by 2021.

A new systematic assessment of developmental neurotoxicity would likely lead to more insecticides being classified as developmental toxicants, including both organophosphates and substances from groups considered as “less toxic”, such as pyrethroids and neonicotinoids. Interestingly, the assessment of developmental neurotoxicity will “cross-talk” with endocrine disruption, as effects on the thyroid function or neuroendocrine axes will primarily impair the cognitive and behavioural development.

Major developments are ongoing on exposure assessment as well. Substances included in the EU residue monitoring programmes do not necessarily cover all residues relevant to dietary risk assessment. Efforts are being made to identify the different compounds resulting from abiotic or biotic transformation of an active substance (and there can be dozens of them), which can sum up with the toxicity of the parent compound or even have a qualitatively different toxicological profile. Therefore, the identification and assessment of
toxicologically relevant residues might disclose that the use of a low-concern active substance could lead to high-concern residues, calling for regulatory measures.

This aspect is relevant also for the evaluation of “negligible exposure”: according to the EU regulation, a substance with high-concern properties (e.g. endocrine disruption) shall not be approved unless the proposed use leads to a negligible (dietary and non-dietary) exposure in humans, where “negligible” can be interpreted as: so small that it can safely be ignored. It is easy to guess that the proposal of a “negligible” exposure can be jeopardised by the incomplete toxicological characterisation of the relevant metabolites.

Moreover, the metabolites formed in the environment participate to the non-dietary exposure of workers, by-standers and residents: one example is ETU, an important thyroid-disrupting metabolite of mancozeb and similar fungicides. Thus, it may be not-so-easy to salvage a hazardous, e.g. endocrine-disrupting, substance by demonstrating that the exposure is negligible.

Cumulative exposure to multiple residues is a long story: The EU residue monitoring plans consistently show that more than 20% of fruit/vegetable samples bear residues of multiple active substances, each individual residue staying within its legally authorised limit. EFSA on 2013 has established that compounds with similar effects in the same target organ may have additive effects, irrespective of chemical structure and molecular mechanism.

The reaction by risk managers has been somewhat slow, however, the work has proceeded, Two draft opinions on cumulative dietary risk characterisation of pesticides that have acute effects on the nervous system and chronic effects on the thyroid have been presented for public consultation (closed on November 15 2019). The exposure assessments used monitoring data collected by Member States under their official pesticide monitoring
programmes. The draft opinions (to be finalised upon the evaluation of the comments received) do not identify concerns for consumer safety.

However, an important caveat, as already mentioned, is that these assessments could not consider a number of toxicologically relevant metabolites that are currently not included in residue monitoring, such as the already mentioned ETU. Thus, it cannot be excluded that the cumulative assessment of pesticide residues might trigger important reactions by risk managers when more appropriate data would be available.

What can be done?

In conclusion, the new insights in the risk assessment of pesticides may trigger i) the reduction of chemical substances authorised for use in plant protection products, and/or ii) important restrictions of use, also to support “negligible exposure”. Some groups of substances (eg organophosphates, conazoles) may be particularly “vulnerable” to the new regulatory developments.

The recent evolution is fully justified by scientific evidence as well as by sound precaution, therefore, would this lead toward safer agriculture? Likely and hopefully yes.
However, let’s everybody keep in mind: safer products and treatments are needed (and quite urgently) to replace the “gaps” triggered by regulatory developments.

To achieve this goal, a science-based approach has to be maintained. In simple words: the higher safety of the proposed alternatives should not be given for “granted” (e.g., because a substance or product is “natural”); conversely, it should be demonstrated by robust models and assessments. At least as important, the efficacy of the alternatives should also be proven otherwise the policymakers could have to face unpleasant options, such as salvaging food availability while weakening food safety.

*Please note: This is a commercial profile