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Abstract: Numerous dermal contact products, such as drugs or cosmetics, are applied on the skin, the first protective barrier to their entrance into the organism. These products contain various xenobiotic molecules that can penetrate the viable epidermis. Many studies have shown that keratinocyte metabolism could affect their behavior by biotransformation. While aiming for detoxification, toxic metabolites can be produced. These metabolites may react with biological macromolecules often leading to sensitization reactions. After passing through the epidermis, xenobiotics can reach the vascularized dermis and therefore, be bioavailable and distributed into the entire organism. To highlight these mechanisms, dermatokinetics, based on the concept of pharmacokinetics, has been developed recently. It provides information on the action of xenobiotics that penetrate the organism through the dermal route. The purpose of this review is first to describe and synthesize the dermatokinetics mechanisms to consider when assessing the absorption of a xenobiotic through the skin. We focus on skin absorption and specifically on skin metabolism, the two main processes involved in dermatokinetics. In addition, experimental models and methods to assess dermatokinetics are described and discussed to select the most relevant method when evaluating, in a specific context, dermatokinetics parameters of a xenobiotic. We also discuss the limits of this approach as it is notably used for risk assessment in the industry where scenario studies generally focus only on one xenobiotic and do not consider interactions with the rest of the exposome. The hypothesis of adverse effects due to the combination of chemical substances in contact with individuals and not to a single molecule, is being increasingly studied and embraced in the scientific community.

International audience; The skin covers almost the entire body and plays an important role in detoxification and elimination of xenobiotics. These processes are initiated following the binding of xenobiotics to the aryl hydrocarbon receptor (AhR), which leads to the expression of several detoxification enzymes. To gain some insights on their impacts on skin cells over time, a temporal transcriptional analysis using gene expression arrays was performed in human primary epidermal keratinocyte (HEK) cells exposed for 6, 24 and 48 h to β-naphthoflavone (βNF), a potent agonist of AhR. Our results demonstrated that expression of genes related to xenobiotic, inflammation, and extracellular matrix remodeling was increased upon βNF treatment from 6 h onwards. In contrast, the anti-oxidative response was seen mainly starting at 24 h. While some of the genes controlled by the epidermal differentiation complex was induced as soon as 6 h, expression of most of the S100 related genes located within the same chromosomal locus and keratin genes was increased at later times (24 and 48 h). Altogether our transcriptomic data highlight that following βNF exposure, HEK cells elicited a protective xenobiotic response together with the activation of inflammation and keratinocyte regeneration. Later on these processes were followed by the stimulation of anti-oxidant activity and terminal differentiation.

Until now, ex vivo human skin explant utilization in tissue culture has consisted of limited short-term studies (less than a week). This short timeframe does not allow for the investigation of metabolic responses of complex tissues to specific molecules or compounds. Here, we aim to develop an improved mouse transplantation model that maintains the viability, structure and functionality of the human skin explants for prolonged periods of time. Healthy human skin explants derived from biopsies were grafted onto nude mice and used to perform a toxicological study of the reactivity and functionality of grafted skin explants after one month. Histological observations suggest that the tissue properties and phenotype of the human skin graft are conserved as a result of re-vascularization upon tissue integration. The toxicological test performed shows that the human skin graft reacts to systemic exposure of a xenobiotic metabolic inducer when applied to this mouse model. This mouse/human chimeric model can be effective for the long-term study of human skin reactivity to chemicals as well to study in vivo responses to complex co-exposures.

In France, andic soils mainly occur in the Massif Central (andic and other volcanic soils >5000 km 2 ), and on the Vosges and the Morvan Hercynian massifs. In the Massif Central, Silandosols on recent pyroclastics are distinguished from Aluandosols on older Mio-Pliocene lavas. After a brief introduction to the parent materials, soil characterisation, survey, genesis, properties and land use are reviewed in two periods: from 1960 to 1979, and from 1980 to 2000. Soil distribution is related schematically to topo-climatic sequences, comparing recent pyroclastics to older volcanic lavas. An udic or perudic soil moisture regime is the primary factor in Andosol genesis in France. Silandosols occur only on recent pyroclastics and Aluandosols on old lavas after reworking by glacial erosion from a mantle of loose and pre-weathered materials. The anthropic impacts include accelerated erosion and changes in carbon content.

Weathering and neoformation of allophane, imogolite and halloysite in volcanic ash soils have been studied extensively in humid climates but little data are available on these soils in arid and semi-arid conditions. Weathering and soil formation under semi-arid conditions on acid pyroclastics have been investigated in two profiles, both at the micro-site scale and on bulk samples. XR microdiffraction and SEM-EDX microanalysis were performed on soil thin sections. Chemical, particle-size, XRD and mineral identification analysis were performed on conventional soil samples. Results show the interplay of various sub-processes : intense division of the coarse minerals into small fragments 50-200 micrometers in size ; diagenesis of noncrystalline products in the zone of contact with the parent minerals ; transformation of noncrystalline minerals into halloysite in the compact soil microstructures and preservation of the noncrystalline minerals in the topsoil ; desiccation and condensation of the crystalline and noncrystalline minerals into microaggregates in the topsoil. The results of these interacting weathering processes are silty-loam soils with no cohesion and high susceptibility to wind erosion. Differences appearing between different analytical methods at different sampling scales need special precautions in explaining the results. (Résumé d'auteur)

The proposed criteria for andosol classification in the World Reference Base (WRB) of Soil Resources were evaluated using the Tohoku University World Andosol Database (TUWAD). The WRB proposal defines a diagnostic andic horizon comprised of vitr-andic, alu-andic, and sil-andic subtypes, and eight second level soil units. Several notable refinements to the WRB criteria were apparent from evaluation of soil properties from TUWAD and are proposed as revised criteria. Our analysis indicated that the most effective criteria for differentiating the andic horizon were glass content, phosphate retention, oxalate extractable Al and Fe, pyrophosphate-extractable Al, and bulk density. The vitr-andic horizon is distinguished by its low degree of weathering, evident from its low oxalate extractable Al and Fe, low P retention, and high glass content. The ratio of pyrophosphate to oxalate extractable Al is used to separate andic horizons dominated by Al-humus, complexes (alu-andic, Al(p)/Al(o) greater or equal than 0.5), from those dominated by allophanic materials (sil-andic, Al(p)/Al(o) < 0.5). When Al(p) data are not availabe, the Si(o) value of 0.6 could be used as an approximate criteria. We also propose revisions to the nine second level soil units based on the dominant pedogenic processes occurring in andosols : non-crystalline material formation and organic matter accumulation. These soil units are based on the degree of weathering (oxalate extractable Al, Fe, glass content), the dominant weathering agent (organic acids vs. carbonic acid), type (melanic or fulvic) and quantity of organic matter, and high 1.5 MPa water-holding capacity. The revised criteria determined by this study effectively differentiate andosols based on their dominant pedogenic processes, and the relationship or soil properties to productivity and utilization. (Résumé d'auteur)

Soil sequences derived from Tertiary and Quaternary volcanic rocks in the Canary Islands have been investigated according to their exposure being to the north or to the south and to altitude. Some of the soil characteristics are described, emphasising the evolution in the sequences and the conditions of genesis. The northern sequence is divided into two parallel catenas, the differences in which are due to the age of parent materials. From top to bottom, the old sequence includes ferrallitic soils, fersiallitic soils and finally vertisols. The Recent sequence, includes andosols and brown soils. Thus, the distribution is related with climatic altitudinal zonality: perhumid at the top, then contrasted (with alternating humid and dry seasons) and finally subarid near the coast; this zonality is also reflected by the plant geography. The relationships between soils and present-day climatic zones are evident for Recent formations: andosols and perhumid climate, brown soils and contrasted climate. These relationships seem equally plausible for the more ancient formations. The authors suggest a direct lineage between unsaturated andosols and ferrallitic soils on the one hand, and between brown soils and fersiallitic soils on the other. The southern sequence comprises, successively from the top downwards: andic brown soils, typic brown soils, fersiallitic soils, vertisols, cinnamonic soils and sodic soils. Because of a much lesser deposition of Recent volcanic material, only one sequence can be noted. The soil distribution is also related to a climatic and vegetational altitudinal zonality. Moreover, the sequence has a greater extension towards the arid pole, because the south slope is less rainy than the north. The relationships between soil genesis and existing climatic conditions still seem very plausible for the upper part of the sequence, especially the andic brown, the typic brown and the fersiallitic soils. In the lower part of the sequence, however, the authors suggest that the evolution is related to the fluctuations of Quaternary climate. At the time of the last fluctuation, after a more humid climate favoring clay formation, there followed an increasingly arid climate producing calcium carbonate accumulation, gypsum and finally sodification of soils as well as genesis of palygorskite.

Not available, Au Mexique, le mot tepetate désigne certains horizons indurés de cendres volcaniques, à consistance de roche, mis à nu par l'érosion anthropique des sols. Les tepetates étudiés ici se localisent au piémont de la Sierra Nevada, dans une zone climatique semi-aride à saison sèche de 5 à 6 mois et pluviosité de 600 à 800 mm/an. La consistance dure à l'état sec s'explique par le fait que le matériau originel du tepetate est un tuf. La cohésion de la matrice est renforcée par l'empilement des minéraux argileux (interstratifiés 1:1/2:1) en plaquettes orientées face à face. Un drainage restreint a provoqué l'accumulation d'argiles illuviées et éventuelle d'oxyhydroxydes de fer et de manganèse, qui colmatent une partie des macropores et des fissures. L’intercalation de silice non cristalline (gel, opale A) a renforcé l'arrangement déjà compact hérité du tuf. La présence d'argiles 2:1 smectitiques et le cycle annuel des saisons humide et sèche sont responsables de la variation des propriétés du tepetate de type fragipan, à savoir: dureté à l'état sec, friabilité et plasticité à l'état humide

Not available, Au Mexique, le mot tepetate désigne certains horizons indurés de cendres volcaniques, à consistance de roche, mis à nu par l'érosion anthropique des sols. Les tepetates étudiés ici se localisent au piémont de la Sierra Nevada, dans une zone climatique semi-aride à saison sèche de 5 à 6 mois et pluviosité de 600 à 800 mm/an. La consistance dure à l'état sec s'explique par le fait que le matériau originel du tepetate est un tuf. La cohésion de la matrice est renforcée par l'empilement des minéraux argileux (interstratifiés 1:1/2:1) en plaquettes orientées face à face. Un drainage restreint a provoqué l'accumulation d'argiles illuviées et éventuelle d'oxyhydroxydes de fer et de manganèse, qui colmatent une partie des macropores et des fissures. L’intercalation de silice non cristalline (gel, opale A) a renforcé l'arrangement déjà compact hérité du tuf. La présence d'argiles 2:1 smectitiques et le cycle annuel des saisons humide et sèche sont responsables de la variation des propriétés du tepetate de type fragipan, à savoir: dureté à l'état sec, friabilité et plasticité à l'état humide