Formulation of water pollutant discharge limits based on nonsensitive aquatic organism protection

Abstract

The “Integrated Wastewater Discharge Standard” was implemented for water pollutant discharge in China’s pesticide industry, which has no control requirements for particular wastewater pollutants in the industry. In the standard, certain pollutants discharge limits are limited strictly or loosely, resulting in practical management implementation difficulties. In view of the highly selective targeting characteristics of organic pesticide active ingredients in fungicides, insecticides, and herbicides, a method for deriving discharge limits based on the water quality criteria for pesticides for the protection of nonsensitive species is established based on the idea of fully protecting aquatic organisms beyond sensitive objects.

Through the use of malathion (Malathion is  a man-made organophosphate insecticide  that is commonly used to control mosquitoes and a variety of insects that attack fruits, vegetables, landscaping plants, and shrubs. It can also be found in other pesticide products used indoors and on pets to control ticks and insects, such as fleas and ants) as an example, by screening its toxicity data in different species of aquatic organisms, the sequence point with the most significant change in the acute toxicity sensitivity of the species is taken as the variation point in the cumulative frequency of the sensitive and nonsensitive species to derive the water quality criteria, using the species sensitivity distribution method as the scientific basis for determining the discharge limits. After a comparative analysis of different simulation models, the sigmoid model, with the best fit, is selected to determine that the sensitive species hazard concentration (HCs) of malathion to aquatic organisms in China is 46.4 µg/L, and the discharge limit derived from the HCs based on the relationship between the environmental capacity and emissions is rounded to 250 µg/L. Studies showed that the relationship between the emissions limit derived from the water quality criteria for protecting nonsensitive species and malathion limit stipulated in the “Environmental Quality Standards for Surface Water” conforms to the corresponding relationship of the quality standard and discharge standard, which can be achieved by current pollution control technology, combined with water quality improvement. The discharge limit offers the advantages of technical accessibility and economic rationality.

Introduction

Pesticides are an important means of production and widely used in agriculture, forestry, health, and other fields for controlling pests. China is a leading country in the production and use of pesticides, with the national pesticide output reaching 2.498 million tons in 2021. Pesticides can guarantee food security and agricultural product quality but also pose a threat to the ecological environment. Currently, enterprises manufacturing pesticides other than heterocyclic pesticides are subject to the “Integrated Wastewater Discharge Standard1” and provinces with local standards are subject to local pollutant discharge standards. The Ministry of Ecology and Environment is currently formulating a discharge standard for water pollutants for the pesticide industry and solicited public opinion for the second time in March 2022.

There are two common approaches in the regulation of wastewater discharges standard: technology-based and water-quality-based standards. The technology-based standards mainly reflect the level of pollution prevention and control technology requirements, and are difficult to combine with the water quality of specific watersheds. The water quality-based discharge standards has certain advantages in connecting with the goal of improving water environment quality, and are closely related to water environmental quality standards. Water quality criteria refer to the maximum acceptable dose (or harmless effect dose), concentration level, or pollutant limit in an aquatic ecological environment with certain natural characteristics with no harmful effects on specific objects (aquatic organisms or people). Water quality criteria are the scientific basis for deriving water quality standards and environmental quality standards and further formulating discharge standards. In recent years, with the increasing application of environment-friendly, efficient, low-toxicity, and low-residue pesticides, preliminary research found that the main varieties of pesticides in China have low toxicity to human health. However, all varieties of pesticides, such as insecticides, herbicides, and fungicides, are highly toxic to specific sensitive aquatic organisms. The technology-based discharge limits cannot effectively prevent and control environmental risks to aquatic organisms. Therefore, it is necessary to derive discharge limits based on water quality standards, and the establishment of water quality standards requires the derivation of water quality criteria. For this reason, the establishment of water quality criteria with the main goal of protecting aquatic organisms is the key to examining pesticide water quality standards. To further standardize the derivation of water quality criteria for freshwater organisms, the Ministry of Ecology and Environment issued the “Technical Guidelines for Deriving Water Quality Criteria for Freshwater Organisms” in 20222. The Ministry of Ecology and Environment of China issued three freshwater organism water quality criteria, including for cadmium, ammonia nitrogen, and phenol, as well as nutrient criteria for lakes in the central and eastern lake regions in the country3. In recent years, at home and abroad systematically examined the theoretical methodology of water quality criteria and developed water quality criteria for different varieties of pollutants. On the basis of common methods implemented at home and abroad, it was determined that 95% of species must be protected in the derivation of the water quality criteria for aquatic organisms. However, living organisms are extremely sensitive to pesticide active ingredients. The criteria value and discharge limits derived based on the protection of 95% of species will be extremely strict and will not comply with the technical process for formulating discharge limits based on the principle of technical feasibility and will not be economically reasonable. Therefore, a method for determining discharge limits for pesticide active ingredients must be established to not only connect with protection objectives and water body functions but also offer economic and technical feasibility with a scientific basis.

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Taxonomy

• Pesticides
• Fertilizers and Pesticides
• Pesticides