Application of a soil quality assessment system using ecotoxicological indicators to evaluate contaminated and remediated soils.

The deterioration of soil quality owing to human activities results in adverse effects on the soil ecosystem. This study developed a systematic method to quantitatively evaluate soil quality based on physical, chemical, biological, and ecotoxicological indicators and proposed the soil quality assessment and management system. This system consists of step-by-step processes, including indicator classification, indicator measurement, scoring and weighting, and soil quality index (SQI) calculation. The novel strategy included the usage of authentic ecotoxicological indicators for realistically interpreting soil quality assessment results. This study used five ecotoxicological indicators, including earthworm survival, enzyme activities, nematode reproduction, plant germination and growth, soil algal biomass, and soil algal photosynthetic capacity. Relatively higher SQI values than those corresponding to the actual soil quality status would be obtained without considering the ecotoxicological indicators. We conclude that the use of ecotoxicological indicator can help in soil quality assessment even under extreme soil quality conditions, such as highly contaminated or physically and chemically remediated soils.

Development of a nematode offspring counting assay for rapid and simple soil toxicity assessment.

Since the introduction of standardized nematode toxicity assays by the American Society for Testing and Materials (ASTM) and International Organization for Standardization (ISO), many studies have reported their use. Given that the currently used standardized nematode toxicity assays have certain limitations, in this study, we examined the use of a novel nematode offspring counting assay for evaluating soil ecotoxicity based on a previous soil-agar isolation method used to recover live adult nematodes. In this new assay, adult Caenorhabditis elegans were exposed to soil using a standardized toxicity assay procedure, and the resulting offspring in test soils attracted by a microbial food source in agar plates were counted. This method differs from previously used assays in terms of its endpoint, namely, the number of nematode offspring. The applicability of the bioassay was demonstrated using metal-spiked soils, which revealed metal concentration-dependent responses, and with 36 field soil samples characterized by different physicochemical properties and containing various metals. Principal component analysis revealed that texture fraction (clay, sand, and silt) and electrical conductivity values were the main factors influencing the nematode offspring counting assay, and these findings warrant further investigation. The nematode offspring counting assay is a rapid and simple process that can provide multi-directional toxicity assessment when used in conjunction with other standard methods.

Rapid in situ assessment for predicting soil quality using an algae-soaked disc seeding assay.

The soil quality of remediated land is altered and this land consequently exerts unexpected biological effects on terrestrial organisms. Therefore, field evaluation of such land should be conducted using biological indicators. Algae are a promising new biological indicator since they are a food source for organisms in higher soil trophic levels and easily sampled from the soil. Field evaluation of soil characteristics is preferred to be testing in laboratory conditions because many biological effects cannot be duplicated during laboratory evaluations. Herein, we describe a convenient and rapid algae-soaked disc seeding assay for assessing soil quality in the field based on soil algae. The collection of algae is easy and rapid and the method predicts the short-term quality of contaminated, remediated, and amended farm and paddy soils. The algae-soaked disc seeding assay is yet to be extensively evaluated, and the method cannot be applied to loamy sand soil in in situ evaluations. The algae-soaked disc seeding assay is recommended for prediction of soil quality in in situ evaluations because it reflects all variations in the environment. The algae-soaked disc seeding assay will help to develop management strategies for in situ evaluation.