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30Heavy metals such as cobalt, copper, manganese, molybdenum, and zinc are essential in trace 31 amounts for growth by plants and other living organisms. However, in excessive amounts these 32 heavy metals have deleterious effects. Like other organisms, plants possess a variety of 33 detoxification mechanisms to counter the harmful effects of heavy metals. These include, the 34 restriction of heavy metals by mycorrhizal association, binding with plant cell wall and root 35 excretions, metal efflux from the plasma membrane, metal chelation by phytochelatins and 36 metallothioneins, and compartmentalization within the vacuole. Phytoremediation is an emerging 37 technology which uses plants and their associated rhizospheric microorganisms to remove 38 pollutants from contaminated sites. This technology is inexpensive, efficient and ecofriendly. 39 This review focuses on potential cellular and molecular adaptations by plants that are necessary 40 to tolerate heavy metal stress.41 42

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Preliminary analysis was performed to assess human health risks of exposure to 16 polycyclic aromatic hydrocarbons (PAHs) by way of inhalation by children and adults living in urban area of Amritsar, Punjab, India. In particular, the United States Environmental Protection Agency's (USEPA's) 16 priority PAH compounds were analyzed in air particulate matter (PM10) from different geographical locations by high-volume air sampler. Sum concentrations of PAHs (37-274 ng m(-3)) were comparable with those of other cities in India as well many cities on a global scale. Pyrene, naphthalene, acenaphthene, acenaphthylene, fluoranthene, fluorene, and dibenzo(a,h)anthracene accounted for >80% of ∑16PAH concentrations. Furthermore, the contribution of seven carcinogenic PAHs accounted for 12% of ∑16PAHs. The estimated carcinogenicity of PAHs in terms of benzo(a)pyrene toxic equivalency (BaPTEQ) was assessed and confirmed that dibenzo(a,h)anthracene was the dominant PAH contributor (88.7%) followed by benzo(a)pyrene (6.67%). Homolog pattern and diagnostic ratios of PAHs suggested that mixed pyrogenic sources--including biomass burning, coal combustion, and petrogenic sources, such as vehicular emissions--are dominant PAH sources in Amritsar. Health risk of adults and children by way of PAHs was assessed by estimating the lifetime average daily dose (LADD) and corresponding incremental lifetime cancer risk (ILCR) using USEPA guidelines. The assessed cancer risk (ILCR) was found to be within the acceptable range (10(-6)-10(-4)).

Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) were determined in agricultural soils from the northern states of India. The average concentration of OCPs was 37.67 ± 0.33 ng/g (dry weight − DW) while HCHs alone accounted for 93% followed by DDT (4.27%) and endosulphan (2.51%). The α/γ ratio of HCH (< 0.01–8.64) reflects the use of technical as well as lindane formulations. The ratio of p,p’-DDT/p,p’-DDE (0.16) and o,p’-DDT/p,p’-DDT (< 0.01) indicates the contamination of soils with the past use of technical DDT. The mean concentrations of endosulphan and dieldrin were 0.95 ± 0.53 ng/g (DW)and 0.16 ± 0.07 ng/g (DW), respectively. The average concentration of PCBs was 13.44 ± 0.06 ng/g (DW). The toxic equivalency (TEQ) calculated using WHO 2005-TEFs ranged from 0.01 to 105.40 pg WHO 2005-TEQ/g (DW) with the mean of 13.78 ± 0.11 pg WHO 2005-TEQ/g (DW). PCB-105 (25%), PCB-114 (18%), and PCB-118 (18%) were the dominant congeners and accounted for 61% while a non ortho PCBs contributed only 18% to total DL-PCBs. The contamination of soils is a matter of concern but is not alarming because the observed levels were lower than those given by the Canadian soil quality guidelines.