Agricultural irrigation using wastewater containing heavy metals (HM) might impose risks in bioaccumulation in foods. The current study was performed to assess the status of HM in terms of water-soil−plant systems in Kandahar, Afghanistan, where industrial and domestic wastewater was partially reused for irrigation. Water, soil, and plant samples were collected from wastewater sites in Haji-Arab (HA), Bala-Karz (BKZ), and Mahal-e-Nejat (MN) in comparison with those from a freshwater-irrigated site in Char-Bagh (CB). The HM levels in unfiltered water samples remained lower than the World Health Organization (WHO) and Food and Agriculture Organization (FAO) permissible values, but the HM concentrations in soil and crops were higher at the HA, BKZ, and MN (wastewater-irrigated sites) than those at the CB site (freshwater-irrigated site). Lead (Pb) levels were high in soils (43−83 mg/kg) and crops (18−36 mg/kg) and extremely exceeded the safe limits even for those crop samples cultivated in the freshwater-irrigated site. Continuous wastewater irrigation increased the HM concentration in water, soil, and plants, but the Pb pollution was found to be ascribed to the minerals in that area since the underground water was showing high Pb levels. The bioaccumulation of HM in the studied sites was related to the cultivated crops and correlated with the land use in the watershed area. This study is important in understanding the risks associated with HM and exercising prudence when applying various irrigation resources in Afghanistan.

Chemical analysis (about 20 parameters) of the leaves of 37 plants representative of the Mediterranean mattoral reveals a clear biochemical and ecological structuration. This phytochemical organization could be dependent on the synecological relationships between plants and herbivores («T» and «a» tactics). Even if the tannin plant frequency is here relatively low (about half of the species), these defensive molecules are particularly effective owing to the development of the phenyl-trihydroxylation. Tanniferous plants are significantly richer in total phenols and cellulose, but reversely poorer in proteins, soluble sugars, potassium and magnesium. On an other defensive level, the most sclerophyllous plants are significantly poorer in proteins, potassium and phosphore and somewhat richer in lignin. Multivariate analysis firstly opposes the plants rich in phenolic substances (Ericaceae) to those rich in nitrogen and potassium (Papilionaceae). Both sclerophylly and - with opposite signs - alimentary value are found on the same structuring axis, which confirms the synecological determinism of the recorded organization. Moreover, the classic C/N ratio appears as a common feature of this phytochemical gradient and links this part of the ecosystem to its pedological substrate. A short comparison is made with other phytocenosis, located in severe or not severe environments, initiating a more general approach of the structuration of the phytocenosis in the frame of the bioenergetic allocations.

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