Determining toxicity of lead and zinc runoff in soils: Salinity effects on metal partitioning and on phytotoxicity

• Published in: Environmental toxicology and chemistry 2003-12, Vol.22 (12), p.3017-3024
• Main Authors: Stevens, Daryl P., McLaughlin, Mike J., Heinrich, Tundi
• Format: Article
• Language: English
• Subjects: Aluminum Silicates; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Clay; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on plants and fungi; Effects of pollution and side effects of pesticides on protozoa and invertebrates; Fundamental and applied biological sciences. Psychology; Hydrogen-Ion Concentration; Lactuca; Lactuca sativa; Lead; Lead - chemistry; Lead - toxicity; Lethal Dose 50; Lettuce; Metal phytotoxicity; Salinity; Sodium Chloride - pharmacology; Soil Pollutants - toxicity; Tissue Distribution; Water Pollutants - toxicity; Zinc; Zinc - chemistry; Zinc - toxicity
• ISSN: 0730-7268; 1552-8618
• DOI: 10.1897/02-290

When assessingcationic metal toxicity in soils, metals are often added to soil as the chloride, nitrate, or sulfate salts. In many studies, the effects of these anions are ignored or discounted; rarely are appropriate controls included. This study used five soils varying in pH, clay content, and organic matter to determine whether salinity from counter‐ions contributed to or confounded metal phytotoxicity. Varying rates of Pb and Zn were applied to soils with or without a leaching treatment to remove the metal counter‐ion (NO3‐). Lactuca sattva (lettuce) plants were grown in metal‐treated soils, and plant dry weights were used to determine median effective concentrations where there was a 50% reduction in yield (EC50s) on the basis of total metals measured in the soil after harvest. In two of the five soils, leaching increased the EC50s significantly for Zn by 1.4‐ to 3.7‐fold. In three of the five soils, leaching increased the EC50s significantly for Pb by 1.6‐ to 3.0‐fold. The shift in EC50s was not a direct result of toxicity of the nitrate ion but was an indirect effect of the salinity increasing metal concentrations in soil solution and increasing its bioavailability for a given total metal concentration. In addition, calculation of potential salinity changes in toxicological studies from the addition of metals exhibiting strong sorption to soil suggested that if the anion associated with the metal is not leached from the soil, direct salinity responses could also lead to significant overestimation of the EC50 for those metals. These findings question the relevance of the application of single‐metal salts to soils as a method of assessing metal phytotoxicity when, in many cases in our environment, Zn and Pb accumulate in soil over a period of time and the associated counter‐ions are commonly removed from the soil during the accumulation process (e.g., roof and galvanized tower runoff).