Information about micronutrient concentrations of plants in general can be found in botany and plant physiology textbooks, but micronutrient concentrations in field-grown lettuce is hard to find and so are concentrations of heavy metals. Lettuce consumers may be concerned with heavy metal concentrations and information about heavy metal concentrations may help consumers make a choice. This study examined the concentrations of eight micronutrients and five heavy metals in field-grown lettuce with different fertilization programs. Under the field conditions, different NPK fertilizers and fertilization rates did not differ in the leaf concentrations of micronutrients and heavy metals. The overall means of Fe, Na, Mo, and Ni concentrations in the lettuce were 663, 710, 0.9, and 1.9 μg·g–1 of dry leaves, respectively. These values were significantly higher (over 500% greater) than the values found in textbooks for plants in general. Mean Mn, Cu, B, and Zn concentrations were 55.5, 7.3, 23.7, and 28.4 μg·g–1 of dry leaves, respectively, which are in general agreement with textbook values. Mean concentrations of heavy metals Cd, Co, Cr, and Pb were 1.5, 1.0, 2.9, and 4.5 μg·g–1 of dry leaves, respectively, whereas mean Al concentration was 498.5 micrograms per gram of dry leaves. These results indicate that concentrations of some elements in lettuce leaves can be high under certain field conditions. It would be beneficial for lettuce growers and consumers to have this information.
Ekaterina A. Jeliazkova, Valtcho D. Jeliazkov, Lyle E. Craker, and Baoshan Xing
Phytoremediation has been suggested as a solution to heavy metal—polluted soils, but the choices of suitable plant species for phytoremediation have been limited. Medicinal and aromatic plants appear to be excellent selections for these plantings, since these plants are grown for economically valuable secondary products (essential oils), not for food or feed. Preliminary research indicates that heavy metals are not accumulated in essential oils, permitting the oil to be used commercially. Productivity of some, but not all aromatic plants was reduced, however, by the heavy metals. The objective of our experiment was to distinguish the mechanism of heavy metal tolerance of plants using germinating seeds of medicinal and aromatic plant species. Seeds from medicinal and aromatic plants were germinated in solutions with selected levels of heavy metals (cadmium at 6 and 10 (μg·L-1; copper at 60 and 150 μg·L-1; lead at 100 and 500 μg·L-1; zinc at 400 and 800 μg·L-1) and in distilled water. Tests on Anethum graveolens L., Carum carvi L., Cuminum cyminum L., Foeniculum vulgare Mill., Pimpinella anisum L., Ocimum basilicum L., and the hyperaccumulator species Brassica juncea L. and Alyssum bertolonii established that different plant species reacted in different ways to the heavy metals. For example, cadmium did not decrease seed germination of Alyssum, O. basilicum, and B. juncea compared with germination in water but did decrease germination of C. cyminum. Lead did not affect germination of A. bertolonii and B. juncea as compared with water but did negatively affect germination of P. anisum, F. vulgare, and C. cyminum. Except for B. juncea, F. vulgare, and C. cyminum, copper had a negative effect on germination. Zinc decreased germination in all tested species except B. juncea.
During the expeditions of 1989–92, samples of soil, fruit, and berries were picked up in Kaunas District (central Lithuania) and experimental orchards to determine the content of heavy metals (Cr, Pb, Ni, Zn). They were established by the atomic absorption meter AAS-30. Within in the limits of the industrial center (Kaunas), the content of heavy metals in soil exceeds the background: cadmium, 6 times; lead, 3, 6 times; zinc, 5 times. When fruit trees grow within the city limits, chromium and lead accumulates in the fruit skin and pith. There is probability that increased amounts of heavy metals can accumulate in the flesh. Fruit grown by roads with intensive traffic, as in town zones, accumulate chromium in the pith and lead in the skin. Fruit from trees grown at a distance of 50 to 100 m from the road contained high amounts of chromium and lead in the pith. In all investigated cases, nickel and zinc accumulated in the pith. When fruit trees grow by roads with intensive traffic or within city limits, fruit are contaminated more with chromium than with lead. Consumers should use only the flesh and remove the skin and pith of such fruit. In experimental orchards, different crops accumulated different amounts of diverse heavy metals. In an irrigated area, strawberries accumulated more heavy metals than currants. Heavy metals (Cr, Pb, Ni, Zn) were found in small quantities in the flesh of sour cherries and plums. Microfertilizers (0.1% boric acid applied after flowering) reduced the absorption of heavy metals (especially Cr and Pb) to the plant's reproductive organs.
Pranitha Patil and Sung Park
Heavy metal contamination in the ground and its effects on human health has been a major concern. The objective of this experiment is to determine how cadmium affects transgenic and nontransgenic (control) petunia plants. Initially, the petunia seed germination medium (SGM) was prepared, and petunia seeds were sterilized and cultured on the SGM medium. During the actual experiment, using 8-day-old germinated petunia, the SGM-Cd media containing four different concentrations (0, 50, 100, and 200 μM) of CdCl2 were prepared. Plant growth and survival rates in four concentrations of SGM-Cd media were recorded. Over 20 days of observations, the plants showed two distinct differences: color and growth. For the first few days, all of the plants grew very slowly, but the plants showed marked differences in growth and color at later days. On the final day, 22 Jan., the control plants on 0 μM of CdCl2 grew 4.2 cm, while the transgenic plant grew 2.4 cm and showed a dark shade of green color. The control plants on 50 μM grew 1.38 cm, while the transgenic plants grew 2.2 cm. The control plants on 100 μM grew 1.14 cm, while the transgenic plants grew a total of 1.7 cm. Both control and transgenic plants on 200 μM had similar growth of 0.94 cm and showed very light shade of green color. The hypothesis in this experiment was confirmed because CdCl2 impacted the growth of the control and transgenic plants by stunting the growth of the plant and changing its color. It is also demonstrated here that transgenic plants containing the heavy metal transport (HMT) gene can grow better than control because of the specific HMT gene that allowed the plant to uptake more CdCl2 into the central vacuole.
M. Ozores-Hampton, B. Schaffer, and H. H. Bryan
The effects of amending soil with municipal soil waste (MSW) on growth, yield and heavy metal content of tomato were tested with different irrigation rates. The following MSW materials were incorporated into oolitic limestone soil: 1) Agrisoil compost (composted trash), 2) Daorganite compost (sewage sludge), 3) Eweson (composted trash and sewage sludge), and 4) no MSW (control). Two rates (high and low) were applied to the soil for each compost. There were no significant effects of irrigation rate on any of the variables tested for tomato in 1991 or 1992. Therefore, the lowest irrigation rate appeared to be adequate for optimum tomato production. Plants grown in Daorganite at the lowest rate of 8 t/ha had greater growth and yield than plants grown in the other MSW materials or the control. Agrisoil and Eweson composts did not increase growth or yield, which may have been due to suboptimal application rates of these materials. There were no differences in the concentration of heavy metals in fruit or leaves among MSW materials or rates. MSW rate generally had no effect on root heavy metal concentration, except for Eweson where the high rate resulted in a higher root zinc concentration than the low rate. There were signifant differences in root concentrations of lead, zinc, and copper among MSW materials. Leaf concentrations of all heavy metals tested were within normal ranges for tomato.
Rufus L. Chaney
Depending on the materials used to produce a compost, it will contain lower or higher levels of nutrients and metals. If composts have been appropriately matured, nutrients are in plant-available forms for crop production, and the compost pH will be near neutral. After 25 years of research and development of regulations and advice for biosolids and compost utilization, pretreatment of industrial wastes allows biosolids composts, and composts prepared from biosolids mixed with municipal solid wastes or yard debris to contain levels of microelements needed for plant nutrition but not high levels that could cause phytotoxicity. Composts can supply N, P, K, Ca, Mg, Fe, Zn, Cu, Mn, B, Mo, and Se required by plants or animals. When used in potting media, supplemental N fertilization is usually required, depending on crop requirements. Use of compost can replace other forms of microelements used as fertilizers in media or fields. Detailed evaluation of potential food chain transfer of Cd, Pb, and other elements in composts clearly shows that consumption of 60% of garden foods produced on pH 5.5 soils with 1000 t compost/ha would not comprise risk over a lifetime of consumption, nor would ingesting the composts at 200 mg/day for 5 years. Potentially toxic organic compounds are either destroyed during composting, or bound very strongly by the compost so that plant uptake is trivial. Compost use can be a safe and wise choice for both home and commercial use to replace peat or uncomposted manures, etc. Many states have developed regulatory controls to assure that pathogenic organisms are killed during composting, and that product quality standards are attained that allow marketing for general use in the community.
Weenun Bundithya and Sherry L. Kitto
Thlaspi caerulescens (Brassicaceae), known as a Zn hyperaccumulator, is able to accumulate and tolerate Zn at high concentrations in its biomass. Cell suspension cultures of Thlaspi caerulescens J et C Presl and B. napus `Westar' have been initiated to study the effect of high Zn concentrations on growth and nutrient uptake. Preliminary studies determined the optimal conditions for subculturing and maintaining cultures. Cell suspensions grew best on Murashige and Skoog medium supplemented with B5 vitamins and 1 mg 2,4-D/liter at 0.4 g/25 ml inoculation density, and with a 2-week subculture period. In an initial experiment, cell suspensions were cultured in media containing 1.96 ppm Zn (basal) or 49 ppm Zn (25x). Media and tissue samples were collected at days 0, 4, 7, 10, and 13, and their nutrient content was analyzed by ICP-AES. Thlaspi and Brassica cell suspensions grew equally well on both media. For both species, uptake patterns of Ca, K, Mg, Mn, and P were not significantly different between the two media; however, >97% of the P was taken up within 2 weeks. Zinc concentration was reduced during the first 4 days (lag phase) in the high-Zn medium, with 27% and 41% taken up by the Thlaspi and Brassica cultures, respectively. Thlaspi took up significantly less Zn than did Brassica. By day 13, Thlaspi and Brassica tissue collected from the high-Zn medium contained 10x and 32x, respectively, more Zn when compared to tissue grown on basal medium.
Joohee Lee and Yeh-Jin Ahn
confer tolerances to not only heat, but also multiple abiotic stresses. In this study, we examined the expression and function of DcHsp17.7 under heavy metal (lead ion) and metalloid (arsenate) stresses. Heavy metal and metalloid contamination poses a
Valtcho D. Zheljazkov and Tess Astatkie
up to 5000 years ( Friedland, 1990 ; Kabata-Pendias and Pendias, 1992 ). Phytoextraction appears to be the most suitable and cost-effective alternative to conventional approaches (such as excavation or dredging) for remediation of mildly heavy metal
Huiying Li, Hongji Luo, Deying Li, Tao Hu, and Jinmin Fu
Heavy metal pollution is a worldwide ecological problem because of its impact on plants and animals and ultimately on the health of human beings via the food chain. Lead is one of the most abundant and widely distributed heavy metals because of its