Summary of Toxicity Classification Criteria for Pesticides to Environmental Organisms

Animals relevant to the environmental toxicology of pesticides include fish, daphnia, algae, birds, honeybees, earthworms, soil microorganisms, silkworms, and natural‑enemy insects, among others.

In the series of national standards GB/T 31270–2014 of the People’s Republic of China, detailed criteria are specified for classifying the toxicity of pesticides to more than ten categories of environmental organisms, including fish, daphnia, algae, large crustaceans, birds, honeybees, silkworms, natural enemies, earthworms, soil microorganisms, non‑target plants, and livestock.

Fish toxicity refers to the adverse effects and hazards posed by pesticides to fish, encompassing acute toxicity, chronic toxicity, embryotoxicity, and teratogenicity. In safety assessments, only acute toxicity is typically evaluated, usually expressed as the median effective concentration (TLm) or the median lethal concentration (LC). ₅₀ ) as a metric.

According to the fish 50% lethal concentration LC ₅₀ (96 h) values are used to classify the toxicity of pesticides to fish into four categories:

Daphnia are an important group of aquatic organisms, serving as food for fish and constituting a key link in the aquatic food chain. Due to their high sensitivity to pesticides, the toxicity of these chemicals to Daphnia is often used as an indicator for assessing the environmental safety of pesticides.

The classification criteria for pesticide toxicity to Daphnia are the same as those for fish toxicity, based on the 50% effective concentration (EC₅₀) that inhibits daphnid activity. ₅₀ (48 h), the acute toxicity of pesticides to daphnids is classified into four levels:

According to the median lethal concentration (LC) for large crustaceans ₅₀ (96 h) values are used to classify the acute toxicity of pesticides to crustaceans into four categories:

Algal toxicity refers to the ability of a pesticide to damage algal cells, manifesting as algicidal effects and growth inhibition. It is quantified by the EC₅₀—the concentration at which 50% of the test organisms are affected. ₅₀ It is often used as an important indicator for assessing the environmental safety of pesticides. According to the half‑effective concentration (EC) for algal growth inhibition, ₅₀ (72 h) values are used to classify the toxicity of pesticides to algae into three categories:

Avian toxicity refers to the effects and hazards of pesticides on birds’ growth, reproduction, and physiological and biochemical functions. It encompasses both acute and chronic toxicity; acute toxicity is typically assessed using the LD₅₀. ₅₀ Indicates that, according to the national standard, the acute oral median lethal dose (LD₅₀) of a pesticide to birds is… ₅₀ and acute feeding at the semi-lethal concentration LC ₅₀ , the acute toxicity of pesticides to birds is classified into four categories, as shown in the table below:

Bee toxicity refers to the ability of a pesticide to cause harm to honeybees, and it is expressed in terms of LD ₅₀ or LC ₅₀ Indicates. According to the acute oral and contact toxicity LD50 values for honeybees, LD ₅₀ (48 h), the toxicity of pesticides to honeybees is classified into four levels:

Toxicity to the domestic silkworm refers to the ability of a pesticide to cause harm to the silkworm’s body, typically expressed as LD. ₅₀ or LC ₅₀ It is stated that test data on the toxicity of pesticides to the domestic silkworm are essential for pesticide registration and for guiding safe usage. According to the acute leaf-dipping method, the lethal concentration 50% (LC₅₀) of the pesticide to the domestic silkworm is… ₅₀ (96 h), the acute toxicity of pesticides to the silkworm is classified into four levels, as shown in the table below:

Fumigation tests are primarily conducted under simulated indoor application conditions to assess the safety of sanitary pesticides. If the mortality rate of silkworms exceeds 10%, the product is considered to pose a high risk to silkworms.

Toxicity to natural enemies: In nature, pests and their natural enemies typically maintain a balanced population dynamic. Natural enemies feed on pests, and as pest densities rise, their populations tend to increase accordingly. However, because natural enemies are more sensitive to pesticides than pests, improper pesticide application can lead to massive mortality among these beneficial organisms, allowing pest populations to rebound and proliferate once again. Therefore, understanding the harmful effects of pesticides on natural enemies is a critical component of integrated pest management and ensures the safe and responsible use of pesticides.

Pesticides typically pose a threat to natural enemies, with Trichogramma wasps serving as a representative example. Safety assessments are also conducted for amphibian natural enemies.

(1) Natural enemy: Trichogramma wasp

Based on the safety factor, the safety of pesticides to Trichogramma was assessed, and the risk to Trichogramma was classified into four levels:

(2) Amphibian natural enemies

Taking frogs as an example, based on the pesticide’s LC50 for tadpoles. ₅₀ (96 h), the acute toxicity of pesticides to tadpoles is classified into four levels:

Toxicity to earthworms refers to the harmful effects of a pesticide on earthworms over a short period of time, typically expressed as LC. ₅₀ It is indicated and used to assess the impact of pesticides on soil organisms, based on the pesticide’s LC50 for earthworms. ₅₀ , the acute toxicity of pesticides to earthworms is classified into four levels:

The classification criteria for the toxicity of pesticides to soil microorganisms are as follows:

(1) CO ₂ Absorption method

CO ₂ In the absorption method, the toxicity of pesticides to soil microorganisms is classified into three levels:

a If the added pesticide concentration in the soil remains constant and suppresses soil microbial respiration by 50% within 15 days, it is classified as highly toxic;

b When the pesticide concentration in the soil is increased to ten times the standard level, any cases that achieve the aforementioned inhibition threshold are classified as poisoning.

c If the pesticide concentration in the soil is increased to 100 times the standard level and still achieves the aforementioned inhibition threshold, it is classified as low toxicity; if none of the three treatment levels reach this inhibition threshold, it is likewise classified as low toxicity.

(2) Nitrogen Conversion Method

If, at any time after 28 days of the experiment, the difference in nitrate‑formation rates between the low‑concentration treatment group and the control group does not exceed 25%, the pesticide may be considered to have no long‑term effects on nitrogen transformation in the soil.

According to the pesticide’s half‑maximal inhibitory concentration (EC50) for growth inhibition of non‑target plants. ₅₀ Values are used to classify the toxicity of pesticides to non-target plants into four levels:

Based on the 28-day median lethal concentration (LC) for livestock. ₅₀ (28 d) values are used to classify the short-term dietary toxicity of pesticides to livestock into four categories:

(Source: Yingtai Analysis)