At global scale, awareness about environmental pollution caused by heavy metals is on rise. Sulfur amendments are applicable and cost-effective soil amendments, which can promote and alternatively mitigate ecosystems functions. However, the influence of sulfur amendments on heavy metals phytoextraction from agricultural contaminated soils remains poorly examined. 

In a study published in Environmental Pollution, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences used a systematic meta-analysis to summarize available knowledge on the contribution of sulfur compounds on plants heavy metals uptake from soils media.

They specifically focused on sulfur type and its stress intensity, type of heavy metal, plant species and accumulating organs, and soil pH value. 

The results showed that the direction of plant response to sulfur amendment highly depends on various factors such as type of amended sulfur, the heavy metal type and its stress intensity, plant organs and other experimental conditions such as soil pH value.   

The researchers used a total of 30 articles reporting data on heavy metals in agricultural soils. From those articles, they compiled a total of 524 data points which were used for the meta-analysis. 

They found that the heavy metal phytoextraction increased with the rising sulfur stress, but sulfur type did not significantly affect the metal extraction between sulfur applied and non-sulfur applied treatments. 

However, factors such as metal type, plant genera, plant individual organs (grain, husk, stalks, leaves and roots), and soil pH value significantly influenced the heavy metal uptake. The cadmium, manganese and nickel, and chromium were the most extracted heavy metals under sulfur application. 

Moreover, sulfur application in soil may not affect grain quality and make it safe for human consumption.  

"In the future, the importance of plant organs and combined heavy metals needs to be tested more thoroughly in polluted agricultural soils," said LIU Wenjie at XTBG.