Goncalves et Al. studied the soaking up capacity of Pinus elliottii from H2O contaminated with Cd, lead and Cr and found that its bark is a good absorbent of heavy metals between pH of 5.0 and 7.0.
Ache acerate leafs with a thick epicuticular wax bed are best suited for biomonitors since metals absorbed are non easy leached out ( Mingorance et al. , 2007 as cited by Serbula et al. , 2012 ) . Serbula et Al. ( 2012 ) assessed the metal consumption of Pinus ssp. and Tila ssp.
( Linden ) and concluded that pine acerate leafs are more sentitive to heavy metal pollution and can be used to biomonitor air pollution. The consequences were supported by the fact that the enrichment factors ( EFs ) of pine acerate leafs, for all elements analysed, were higher compared to linden foliages which had an EF value of less than two which is non declarative of pollution. This is due to differences in physical and physiological nature.
1.3.2 Araucaria columnaris
Araucaria columnaris besides known as Coral reef araucaria is a conifer in the Araucariaceae household. It normally grows in warm clime and can achieve 60 m tallness and can be used as a lead index.Ceburnis and Steinnes ( 2000 ) found that conifer acerate leafs can roll up heavy metals from the ambiance but they observed low keeping of the metals and could non happen a correlativity between dirt and root consumption. They therefore concluded that conifer acerate leafs may merely be used near to pollution sites. The same writers were able to demo that Cd and Mn in acerate leafs but non in moss came from dirt.
1.3 Methods of digestion
Microwave digestion is used to fade out heavy metals in the organic molecules prior to analysis by atomic soaking up spectrometry ( AAS ) or inductive coupled plasma ( ICP ) . This is done fade outing a peculiar sum of sample in a strong acid in a closed vas, and raising the force per unit area and temperature through microwave irradiation therefore increasing the velocity of thermic decomposition of the sample, and advancing solubility of heavy metals in solution.
Finally the digested solutions incorporating heavy metals can be analysed through elemental techniques. Different microwave digestion techniques exist and each method is suited different type of sample whether workss, dirt or any other organic affair. This subdivision reports on the different digestion techniques used to analyze works parts.Dahmani-Muller et Al. ( 1999 ) washed and cleaned works samples for 20 proceedingss ultrasonically to take foreign atoms. They were so oven-dried for 15 H at 85oC and grinded and passed through a 500 µm screen. 0.
250 g of this sample was bit by bit warmed with hydrofluoric acid and perchloric acid was added after chilling. The solution was farther heated to dryness and the residue was so redissolved while heating with hydrochloric acid and eventually diluted to 50 milliliter with distilled H2O.Many other surveies made usage of azotic acid for digestion, for case Lobersli and Steinnes ( 1987 ) dried antecedently washed workss at about 60oC before digesting with concentrated azotic acid.
Prior to this the metal degree were estimated by pull outing with 1M ammonium ethanoate pH 7.00 and pH 4.80 depending on the metals to be analysed. Or there is the instance for Burns and Parker ( 1988 ) who digested 1 g of works sample in a solution of 20:20:1 HCLO4, HNO3 and H2SO4 after drying for 48 H at 45oC and crunching. Residues were redissolved in 5ml of 1 % HNO3.Vousta et Al. ( 1996 ) studied trace metals in veggies by drying at 60oC for 4 yearss after rinsing. The samples were so grounded and topographic point in a desiccator prior to supersonic extraction with concentrated HNO3 and HCl.
Vegetables can besides be analysed by drying at 70oC for 72h and digesting 0.5 g of grounded works tissue with 5 milliliters HNO3 in a certain polyvinyl fluoride crucible and left to stand for 2h at room temperature before puting the melting pot in a high force per unit area metal cylinder. The metal cylinder is so placed in an oven at 100oC for 1h and so 170oC for 5h.
Finally extra acid is evaporated on a hot home base at 105oC and the residues are diluted to 50 milliliters and stored at 4oC until ready for analysis. This technique was employed in the research of Cui et al. , 2004. Kachenco and Singh ( 2004 ) besides analysed vegetable samples by rinsing with 0.1 % teepol for 15 seconds, 0.1 % hydrochloric acid for 15 seconds and eventually three times with deionised H2O. Once clean, the samples were dried at 70oC in a dehydrator for 48 to 72 Hs depending on sample size.
They were so weighed and grinded for digestion in a mixture of azotic acid, perchloric acid.The survey of metals in the rings of Pinus sylvestris were studied by Lukaszewski et al. , 1988 and VanA›k et Al. ( 2010 ) . The former digested 0.5 g of the grounded tree rings with H peroxide and azotic acid ( Douy et al. , 2003 ) after drying for 24 H at 105oC. The latter besides dried the sample for 24h but at 70oC and digesting nightlong with concentrated azotic acid at 190oC in 60 milliliters PTFE beakers.
The solution obtained was dissolved in deionised H2O.In the instance of Zheljazhov et Al. ( 2008 ) medicinal workss were dried at 35oC until they attained a changeless weigh and farther dried at 70oC for 3 yearss and passed through a 1 millimeter screen and stored in closed phials before digesting 1g subsample in 10 milliliters azotic acid in a digestion tubing overnight at room temperature. The mixture obtained was so decomposed on aluminum digestion block at 150oC for eight hours, filtered and made up to 50 milliliters in a volumetric flask with twofold distilled H2O.
Aznar et Al. studied metal taint in lichen. Each sample was cleaned, dried and freeze-dried in a 0.1 g aliquot and transferred in Savillex Teflon bombs with 5 milliliters tridistillated azotic acid and 1 µl fluohydric acid. Digestion was carried out in a high force per unit area autoclave for three hours at 110oC.Nicolaidou and Nott ( 1998 ) used a similar digestion method as used by Bryan et Al. ( 1985 ) by drying the workss at 80oC and digesting with ‘Aristar ‘ HNO3 followed by vaporization before redissolving in 1N ‘Aristar ‘ HCl.
1.4 Analysis of metals
The finding of heavy metals in the works samples are normally done by fire or graphite atomic soaking up spectrometry with extras, spaces and certified mention stuffs ( Yang et al. , 2011 ) . Graphite furnace AAS is normally used to analysed metals falling below the standard divergence of clean samples ( Zheljazkov et al. , 2008 ) . Inductively conjugate plasma can besides be used.
1.5 Consequences from old surveies
Most surveies of impact of smelters on workss found elevated degrees of heavy metals. About all samples analysed exceeded maximal degree allowed, for case, Cd and lead were above the Australian Food criterions maximal degree ( Kachenko and Singh, 2005 ) . Aznar et Al. ( 2007 ) even found Cd, Cu and Pb taint 20 kilometer from the smelter to be two times higher than those at the mention sites ( 50km off ) .
Many surveies showed that taint occurred from atmospheric deposition of heavy metals on the works surface. Aznar et Al. ( 2007 ) found that air current strength, lift and distance from smelter affected the degree of Cd, Cu and lead on workss. Airborne deposition was besides observed by Vousta et Al. ( 1996 ) , Vanek et Al. ( 2010 ) and Kachenko and Singh ( 2005 ) .
Douay et Al. ( ) found that lead content decreased well after smelter closedown accounting one time once more for superficial sedimentations of heavy metals.The countries around smelters are frequently subjected to acid rain ensuing from pollutants such as SO2 in the ambiance. Soil pH besides affects the handiness of metal uptake by workss. Kozlov et Al. ( 1995 ) demonstrated that the degree of manganese fell with increasing distance largely due to high sourness of the dirt caused by acerb rain in the locality of the smelter, this leads to direct leaching of Mn.
Lobersli and Steinnes ( 1987 ) observed that low pH lead to higher handiness of Fe in works. Kachenko and Singh ( 2005 ) observed high consumption of Cd due to sourness of dirt.Some surveies found a relationship between the degree of metal in dirt and workss. The degree of Zn, lead, Cd and Cu in works tissues depend on their concentrations in dirt ( Kachenko and singh, 2005 ) . Low Ni and Cu sedimentations on workss suggested that these metals were largely taken up from the dirt ( Kozlov et al. , 1995 ) . Douay et al.
, ( ) came to the decision that Cd content in wheat grains depended on its degree in dirt since the smelter closure did non take to a noticeable lessening of the element concentration. Lukaszewski et Al. ( 1988 ) besides observed the same consequence in tree rings of Pinus sylvestris L. ) .Kachenko and Singh ( 2005 ) found interactions between Cd and Zn in workss. For illustration, high concentrations of Zn in dirt resulted in high Cd consumption by leafy veggies. Kozlov et Al.
( 1995 ) noted that for high degrees of Cu in workss, the Zn consumption was low.Different works species have different accretion capacity ( Arunachalam et al. , ) . Ostrich fern is considered as an collector since it can absorb 10 times the concentrations observed in Interrupted fern ( Burns and Parker, 1988 ) . Familial differences among species account for the conveyance heavy metals every bit good as accretion in different works parts ( Zheljazkov et al. , 2008 ) .
Furthermore, the physical and chemical construction of the works may alter over clip, therefore the consumption of heavy metals will be different from twelvemonth to twelvemonth ( Watmough and Hutchinson, 2002 ) .Table 1 shows the concentration of metals observed in different works species grown nears smelters.