2.1. Experimental materials
Two types of fresh and living earthworms were procured for use at the experimental plot (30°56′-31°35N, 114°23′-114°49E) through online shopping(Figure 1), E. andrei (Wangjun fishing bait flagship store, Zhenjiang, Jiangsu, China), P. guillelmi (Diaokaduo fishing bait flagship store, Nantong, Jiangsu, China). The samples included approximately 2000 individuals per 1000 g of E. andrei and 300–320 individuals per 1000 g of P. guillelmi.For the E. andrei sample individuals, mature earthworms developmentally homogeneous with each individual has 5 cm long, 2 mm in diameter, 0.5 g in weight. For the P. guillelmi sample individuals, immature earthworms developmentally homogeneous with each individual has 7 cm long, 4.5 mm in diameter, 3.3–3.5 g in weight. A 5 L container was prepared to hold 20 earthworms. A plastic cup of approximately 200 mL was prepared with 3 g by weight of the selected household detergent (perfumed soap, washing powder, shampoo, dish washing liquid, bath lotion, or lavatory cleanser) and placed at the center of the container bottom.
Yellow brown soil derived from peanut cultivation fields was passed through an 8-mesh sieve. Yellow–brown soil could belong toTypical Pale Udalfs in USDA soil taxonomy systems and Luvisols or Eutric Planosols in FAO soil taxonomy systems. The bulk density is 1.39–1.62 × 103 kg m−3 5. 100.0 g Yellow–brown soil was balanced to mixture with 100.0 mL water in a glass volumetric cylinder, the volume is 146.0 mL, so the density of the soil sample is 100.0 g ÷ (146.0 mL - 100 mL) = 2.17× 103 kg m−3 .
The six household detergents were purchased from a supermarket, Perfumed soap (Procter & Gamble,Cincinnati,State of Ohio,U.S.A), Washing powder (Nice, Lishui, Zhejiang, China), Shampoo(SLEK, Nanchang, China), Dish washing liquid(Liby, Guangzhou, China), Bath lotion(Procter & Gamble, Cincinnati,State of Ohio, U.S.A), Lavatory cleanser(SUPERB, GUANGZHOU, China).
Composition of the detergents generally include surfactant to decontaminate, such as sodium stearate was used to made solid perfumed soap and liquid bath lotion, petroleum sodium sulfonate was used to made dish washing liquid, the household detergents are mostly alkalinity, except Lavatory cleanser,which is acidic because the main composition include organic acid. Since detailed formula of the composition sometime is a secret of the company, we can not public more detail.
2.2. Experimental design
Experiments were conducted on the experiment plot from July 17, 2021 to July 18, 2021, after rains. Each plastic cup was prepared with 3 g detergent weighed on a balance scale, the cup was placed at the bottom of a 5 L container, and 3 L water was poured into the container.
For the first trial, 20 P. guillelmi individuals were placed in each container, and a dilution of 1‰ (m/v) of the selected detergent was used to immerse the earthworms; immersion in plain water without any detergent was used as the control. The experiment was repeated four times in every trial. The P. guillelmi were replaced with E. andrei, and the same procedure used in the former experiments was repeated. For the second trial, 3 L of yellow brown soil was placed in each container and 20 P. guillelmi individuals were added, which then drilled into the soil. A detergent dilution of 1‰ (m/v) was then used to inundate the soil with the 20 earthworms hidden inside; watered soil sample without any detergent was selected as the control, and the experiment was repeated four times. The same procedure was then repeated by replacing the P. guillelmi with the E. andrei.
The pH values of the dilution solutions and soil mixtures were determined along with the trials.
2.3. Data collection and calculation
The number of surviving earthworms was determined after 4, 14, and 24 h, and their survival rate was calculated. Data were subjected to one-way analysis of variance, and statistical significance of the means was compared using Duncan’s multiple range test at a 5% probability level using SPSS 17.0 software.