Descriptive statistics for heavy metal concentrations in soils by PXRF methods (mg/kg).

<p>Descriptive statistics for heavy metal concentrations in soils by PXRF methods (mg/kg).</p

Classes of soil heavy metal pollution[31–33].

<p>Classes of soil heavy metal pollution[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172438#pone.0172438.ref031" target="_blank">31</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172438#pone.0172438.ref033" target="_blank">33</a>].</p

Prediction scatter plot of pH (a) and VIP scores of optimized PLSR model (b).

<p>Prediction scatter plot of pH (a) and VIP scores of optimized PLSR model (b).</p

Regression of PXRF measurements against ICP-AES analysis for trimmed datasets.

<p>The red, green and blue dotted lines represent the national standard value of heavy metals when pH <6.5, 6.5–7.5 and >7.5.</p

Comparison of heavy metal pollution grade classification between PLSR and chemical analysis.

<p>Comparison of heavy metal pollution grade classification between PLSR and chemical analysis.</p

Comparison between the prediction accuracy of PLSR models with different spectral preprocessing methods.

<p>Comparison between the prediction accuracy of PLSR models with different spectral preprocessing methods.</p

PXRF and portable VNIR analyzers.

<p>PXRF and portable VNIR analyzers.</p

Descriptive statistics for heavy metal concentrations in soils (mg/kg).

<p>Descriptive statistics for heavy metal concentrations in soils (mg/kg).</p

Location of the study area.

<p>Location of the study area.</p