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The interest in charcoal for agricultural use (biochar) has sharply increased in recent years. However, biochar can contain groups of compounds such as polycyclic aromatic hydrocarbons (PAHs) that are considered persistent pollutants, and are formed concomitantly with biochar during its production by pyrolysis. Soil samples were collected in three experimental areas at different intervals (1, 3, 5 or 6 years) after the application of 16 Mg ha −1 of biochar. The total concentrations of PAHs; benzo[ a ]pyrene; and the estimated total cancer risk in biochar treated plots were larger than found in the control ones, but they decreased over time, equaling the control values after three years in the high C content soil (11.2 g C kg −1 soil), or after six years in the low C content soil (6.8 g C kg −1 soil). Nevertheless, the sum of PAH concentrations found in the biochar amended plots, in the range of 15.80–39.40 ng g −1 , were around two orders of magnitude below the limits of prevention established by Brazilian legislation (8100 ng g −1 ) and some European regulations for soils (3000 ng g −1 ) and also lower than the observed in previous studies about biochar amended soils. Our results indicate that, under the conditions evaluated, the application of biochar to soil in the studied proportion (16 Mg ha −1 , every six years) is safe concerning soil contamination by PAHs. [ABSTRACT FROM AUTHOR]

Fifteen polycyclic aromatic hydrocarbons (PAHs) were analyzed in two fractions (< 63 μm and 63–850 μm) of street dust samples collected in different urban areas of Rio de Janeiro and Niterói cities, Brazil. Individual PAH concentrations and total PAH concentrations (∑ PAH) were evaluated considering geographic and particle size distributions, PAH source and cancer risk. In 53% of the samples, ∑ PAH values were higher in the smallest particles than in the largest ones, whereas the inverse was true for 23.5% of the samples. In 23.5% of the samples, both classes of particles showed comparable ∑ PAH. The highest ∑ PAH concentrations were found in areas of limited air dispersion, resulting in PAH accumulation in street dust. The diagnostic ratios and principal component analysis (PCA) indicated a strong influence of pyrogenic sources on PAH concentration, mainly of vehicular emissions. The cancer risk levels for children and adults, for both particulate size fractions (< 63 μm and 63 μm–850 μm), were comparable for dermal contact and by ingestion, and ranged from 10 − 8 to 10 − 6 , whereas in certain cases the cancer risk level for adults by dermal contact was 2 to 3 times larger than for children. The cancer risk levels via inhalation always ranged from 10 − 13 to 10 − 10 , so this exposure pathway was almost 10 4 less severe than through ingestion and dermal contact, and thus negligible. [ABSTRACT FROM AUTHOR]