The PLI is defined as the amount of the applied product multiplied by the toxicity to non-target-organisms. The indicator has the unit “number of applications (toxicity doses) per ha and year”. As special feature, the toxicity of the pesticide (LD₅₀, LC₅₀, determinable for different organisms) is considered in the assessment. The LD₅₀ value is often used to analyse the influence of a certain pesticide on non-target organisms such as the beneficial organism Trichogramma brassicae (Ghorbani et al., 2016). The Load Index thus describes the calculated number of toxic doses in the sold amount of pesticides.

The PLI was developed and is used in Denmark as advancement to the TFI. The PLI was the basis of a new pesticide taxation system with the aim to tax pesticides according to their toxicity. Additionally, for the implementation and effectivity of the indicator, farmers in Denmark are required to upload their pesticide use data, i. e. the annual pesticide statistics. Thus, the PL can be calculated on the basis of pesticide use data rather than on basis of sales data that may not reflect the actual use by farmers. The data can also be used to create maps with detailed information on pesticide use in different regions and to identify hot spots of pesticide use for designing monitoring programmes and launch initiatives to reduce the pesticide load (Kudsk et al., 2018).

The PLI as used in Denmark constitutes of three sub-indicators: the PL for human health, the PL for ecotoxicology PLECO and the PLFATE for the environmental fate. PLECO is calculated on the basis of LC/LD/EC₅₀ values of the active ingredients for acute toxicity to fish, daphnia and earthworms. PL fate is calculated on the basis of the half-life in soil (DT₅₀), the bioaccumulation factor (accumulation of toxic substances in aquatic organisms) and the SCI-GROW index (a model developed by the US-EPA to estimate pesticide concentrations in vulnerable ground water) (Kudsk et al., 2018).

One constraint of the PLI, as with the TFI, is that ecological effects or damages cannot directly be assigned to pesticide applications, since interactions and intermediate steps often have a major influence on pesticide environmental behaviour (Ongley, 1996). Also, the PLI/LI does not include information on exposure risks or buffer zones required for risk mitigation.

The PLI consists of three sub-indicators for human health, ecotoxicology and environmental fate, respectively. For each of the three sub-indicators a pesticide load (PL) is calculated and expressed as the PL per unit commercial product (kg, L or tablet). PL for human health (PLHH) is based on the risk phrases on the product label, while PL for ecotoxicology (PLECO) is calculated on basis of the LC/LD/EC₅₀ values of the active ingredients for acute toxicity to mammals, birds, fish, daphnia, algae, aquatic plants, earthworms and bees and NOEC values for chronic toxicity to fish, daphnia and earthworms. PL for environmental fate (PLFATE) is calculated on basis of the half-life in soil (DT₅₀), the bioaccumulation factor (BCF) and the SCI-GROW index. PL does not consider the actual exposure, i. e. it reflects the relative risks associated with the use of pesticides (Kudsk et al., 2018).