Chemical characteristics of wildfire ash across the globe and their environmental and socio-economic implications

The mobilisation of potentially harmful chemical constituents in wildfire ash can be a major consequence of wildfires, posing widespread societal risks. Knowledge of wildfire ash chemical composition is crucial to anticipate and mitigate these risks. Here we present a comprehensive dataset on the chemical characteristics of a wide range of wildfire ashes (42 types and a total of 148 samples) from wildfires across the globe and examine their potential societal and environmental implications. An extensive review of studies analysing chemical composition in ash was also performed to complement and compare our ash dataset. Most ashes in our dataset had an alkaline reaction (mean pH 8.8, ranging between 6 and 11.2). Important constituents of wildfire ash were organic carbon (mean: 204 g kg-1), calcium, aluminium, and iron (mean: 47.9, 17.9 and 17.1 g kg-1). Mean nitrogen and phosphorus ranged between 1 and 25 g kg-1, and between 0.2 and 9.9 g kg-1, respectively. The largest concentrations of metals of concern for human and ecosystem health were observed for manganese (mean: 1488 mg kg-1; three ecosystems > 1000 mg kg-1), zinc (mean: 181 mg kg-1; two ecosystems > 500 mg kg-1) and lead (mean: 66.9 mg kg-1; two ecosystems > 200 mg kg-1). Burn severity and sampling timing were key factors influencing ash chemical characteristics like pH, carbon and nitrogen concentrations. The highest readily dissolvable fractions (as a % of ash dry weight) in water were observed for sodium (18 %) and magnesium (11.4 %). Although concentrations of elements of concern were very close to, or exceeded international contamination standards in some ashes, the actual effect of ash will depend on factors like ash loads and the dilution into environmental matrices such as water, soil and sediment. Our approach can serve as an initial methodological standardisation of wildfire ash sampling and chemical analysis protocols.

[T and B clonal populations in actinic prurigo, a photodermatosis]

Actinic prurigo (AP) is a chronic photodermatosis in which genetic and immunological factors has been implicated in the pathogenesis of the disease. This work was designed to investigate the existence of clonal populations of T and B lymphocytes in lesions of the labial mucosa and conjunctiva of patients with actinic prurigo. Genomic DNA of three patients with actinic prurigo and controls were analyzed in Southern blots using DNA molecular probes for the b subunit of the T-cell receptor for antigen (TCR beta) and for the heavy chain of immunoglobulin genes (lg-JH). Clonal rearrangements of T-cell receptor genes were detected in biopsy samples taken from the labial mucosa of two patients and of immunoglobulin genes in DNA extracted from the conjunctiva of a different patient. The presence of distinct clonal T or B lymphocyte populations in patients with actinic prurigo indicates that the immune system may play a relevant role in the pathogenesis of the disease.