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Soil Studies: Non-Target Plants and Earthworms

Charles River performs a range of terrestrial ecotoxicology studies in plants and soil organisms.

Regulatory studies that evaluate the effects of agrochemicals on plants and soil may also apply to biocides, industrial chemicals and veterinary pharmaceutical products when there is a risk of environmental exposure. What impact does your product have on surrounding plants and earthworms? Our soil studies can produce the data you need for a successful registration.

Regulatory Requirements

Non-target plants are often exposed to spray-drift following applications to various crops, or in accidental exposure scenarios; regulators require testing on a range of non-target plants covering a range of taxonomic diverse species, for seedling emergence (OECD 208) and/or vegetative vigor (OECD 227), or OCSPP 850.4100 for US registrations. The selection of species will depend on the specific regulatory requirements based on the specific intended use of the product and the regulatory authority concerned. For example, an agrochemical for US registration tested for phytotoxicity by vegetative vigor will normally require 10 species (6 dicot and 4 monocot), with the test item applied at a rate based on the intended maximum field-use rates. The exposure rates for other scenarios are based on the predicted environmental concentration (PEC).

For seedling emergence and early growth, the test item is incorporated into the soil or sprayed onto the soil after seed planting (often with a requirement for analytical confirmation of soil concentration); for vegetative vigor the test item is sprayed onto the seedlings. Observations on phytotoxicity effects such as reduced germination rate, stunted growth, chlorosis, weight of plants etc are carefully followed and reported. Key outcomes are effective concentrations (or rate) of test items causing effects expressed as EC50, EC25 etc.) and the no observed effect concentration (NOEC). Correct study conduct requires suitable soil substrate, climate conditions, lighting, analytical support etc.) as well as adequate historic control data including with reference substances.

Regulators also require data on products that may harm non-target invertebrates that live on the plants or in the soil, like the commonly studied parasitic wasp (Aphidius rhopalosiphi) and predatory mite (Typhlodromus pyri). Charles River’s team has evaluated these species for many years under basic and extended (reproduction) conditions. In these tests, agrochemical products are applied to glass plates or to leaf discs with a laboratory agricultural spray unit, before the arthropod exposure. These tests are now supplemented with the “aged residue” version of the tests as a 3rd tier method where plant are sprayed with a plant protection product at a normal maximal rate, then kept outside protected from rain for a period of days or weeks, then leaf discs are cut and tested as above, to identify how long a product remains toxic before it degrades to a non-toxic form.

Supporting Your Registrations

Supplementing these long-standing assays, our team has recently implemented the soil predatory mite assay (Hypoaspis aculeifer) and will offer OECD 226 commercial testing in early 2021.

Our scientists also have extensive experience in other soil study designs such as the earthworm (Eisenia fetida) acute and reproduction toxicity assays (OECD 207 and 222) and the Collembola (Folsomia candida) reproduction assay (OECD 232). Currently in implementation phase are the carbon transformation and nitrogen transformation tests for soil microorganisms (OECD 217 and OECD 216). These soil assays are all designed to measure potential adverse effects of PPPs and other chemicals, on important soil dwelling organisms, where the LC50 or EC50 and NOEC etc are calculated.

The results of the various tests for toxicity in plants and invertebrates living on them, and in soil, are a key part of any PPP registration, often setting the maximum allowed rates of application. Pharmaceutical and veterinary products that might end up in the environment after excretion can also require specific plant/soil testing; similarly, biocides and industrial chemicals require the same types of tests where significant environmental exposure may occur.

Whether you’re on the drive to register your PPP or need to assess your drug product’s effects on the environment, our team of ecotoxicology experts can help you design and plan a testing program that gathers the data you need to meet regulatory requirements.

Talk to our Team