Selection of plants for phytoremediation of sites contaminated with several metals

Phytoremediation refers to the use of higher plants to rehabilitate contaminated sites without the need to excavate the contaminant material and dispose of it elsewhere. The use of plants capable of taking up high amounts of metals has been proven effective in the rehabilitation of metal-contaminated soils. Plants are grown for a certain period of time and are then harvested and subjected to composting, compaction, incineration, ashing, pyrolysis, direct disposal or liquid extraction. In principle, the best plants for the purpose are those that can tolerate the polluted soil condition, can absorb high amounts of the contaminants, and have economic value (e.g. flowering plants) so that they can also be a source of income. Thus, selection of the suitable plant species is crucial to the success of any phytoremediation program.

In a recent study by HY Lai of MingDao University and and ZS Chen of National Taiwan University published in the International Journal of Phytoremediation, 33 flowering plant species were tested on a 1.3-ha field in central Taiwan. The site is contaminated with multiple metals (As, Cr, Ni, Cu and Zn) due to the continuous irrigation of wastewater from surrounding chemical plants in the last decade. The study used three models for the selection of suitable species: 1) a relative percentage weighting of the growth condition and the metal accumulation capacity of 80% and 20%, respectively; 2) a relative percentage weighting of the growth condition and the metal accumulation capacity of 50% and 50%, respectively; and 3) a relative percentage weighting of the growth condition and the metal accumulation capacity of 0% and 100%, respectively.

The 33 plants included bougainvillea (Bougainvillea spp.), rainbow pink (Dianthus chinensis), serissa (Serissa japonica), French marigold (Tagetes patula), rose of Sharon (Hibiscus syriacus), water willow (Salix warburgu), Chinese ixora (Ixora chinensis), sunflower (Helianthus annuus), Chinese hibiscus (Hibiscus rosasinensis), gold dewdrop (Duranta repens), kalanchoe (Kalanchoe blossfeldiana), creeping trilobata (Wedelia trilobata), garden canna (Canna generalis), garden verbena (Verbena hybrida), Malabar chestnut (Pachira macrocarpa), purslane (Portulaca oloraua), common lantana (Lantana camara), fancy leaf caladium (Caladium xhortulanun), coleus (Coleus blumei), golden trumpet (Allamanda cathartica), common melastoma (Melastoma candidum), Carland flower (Hedychium coronarium), Manaca raintree (Brunfelsia uniflora), yellow cosmos (Cosmos sulphureus), silver apricot (Ginkgo biloba), temple tree (Plumeria acutifolia), orchid tree (Aglaia odorata), star cluster (Pentas lanceolata), blue daza (Evolvulus nuttallianus), cockscomb (Celosia cristata), scandent scheffera umbrella tree (Schefflera arboricola), Bojers spurge (Euphorbia splendens), and croton (Codialum variegatum).

Some of the highlights of the study: Twelve (12) plants out of the 33 tested were selected based on two key factors: 1) ability to tolerate the toxicity of metals (i.e. good growth of the plant) and 2) ability to accumulate high concentrations of metals in the shoot. Using equal weighting (meaning 50% to 50%) of good growth condition (factor No. 1) and of accumulated metal concentrations (factor No. 2), six (6) woody and six (6) herbaceous plant species showed the best potential for phytoremediation of the contaminated site and thus were selected for further testing. These included the following plant species: purslane, garden canna, Bojers spurge, Chinese ixora, croton, kalanchoe, serissa, garden verbena, rainbow pink, French marigold, scandent scheffera umbrella tree, Chinese hibiscus, and sunflower.

The study also revealed that the herbaceous species accumulated higher concentrations of metals and thus have higher “bioconcentration factor” (ratio of metal concentration in shoots to that of the soils) compared to the woody species. The increase of metal concentrations for the herbaceous species were 9.4-fold for Cu, 5.1-fold for Cr, and 8.9-fold for Zn while for the woody species they were 3.1-fold for Cu, 2.5-fold for Cr, and 4.3-fold for Zn.

Reference

Lai HY and ZS Chen. 2009. In-situ selection of suitable plants for the phytoremediation of multi-metals contaminated sites in central Taiwan. International Journal of Phytoremediation 11: 235-250.

Brief history and current state of soil science in the Philippines

First published June 2009. Revised November 2016.

Philippine soil science owes its early development to the Americans. The first soil survey was conducted by C. W. Dorsey an American soil surveyor in 1903. In 1921 a Division of Soil and Fertilizer was created under the Bureau of Science which in 1934 was renamed as Division of Soil Survey. In 1951, the Philippine Congress enacted Republic Act No. 622 organizing the Bureau of Soil Conservation with Dr. M. M. Alicante as its first director (BSWM, 2008). Teaching of soil science to students of agricultural science started as early as the 1920s at the University of the Philippines College of Agriculture (UPCA). R. L. Pendleton an American from California was one of the pioneer soil science instructors who taught from 1923 to 1935. Dr. Pendleton was also an outstanding researcher as reflected by the about 50 scientific papers he published (Pendleton, 1942; Carter, 1958).

Until about the 1960s, much of the work of soil scientists in the Bureau of Soil Conservation (which became Bureau of Soils in 1957) was on soil survey and mapping of soil series in the entire archipelago as well as in promoting soil conservation practices. Because of the major role that soil science played in the green revolution, Philippine soil science enjoyed rapid development in the 1970s and 1980s ("golden age") primarily due to the massive faculty development at the University of the Philippines at Los Banos (UPLB) wherein young faculty members were sent abroad primarily to the U.S.A. for graduate studies, and to the world class soil research that was at the time brewing at the nearby International Rice Research Institute (IRRI) thanks largely to Nyle C. Brady.

N.C. Brady (Source: Facebook.com)

NC Brady of Cornell University who taught at UPCA (now UPLB) as Cornell visiting professor after the war returned to Los Banos in 1973 as the third director general of IRRI and remained there until 1981. During Brady's time (and until now), many leading soil scientists from around the world visited or conducted research at IRRI. Some of the internationally well-known soil scientists who worked at IRRI included P.A. Roger (France), H.U. Neue and H.W. Scharpenseel (Germany), F.N. Ponnamperuma (Sri Lanka), T. Yoshida and I. Watanabe (Japan), N. van Breemen and F. Moormann (Netherlands), D.J. Greenland and G.J.D. Kirk (U.K.), R. Bloom and P.A. Sanchez (USA), and S. Sombatpanit (Thailand). By establishing a world class soil research at IRRI and through his soil science textbook (Nature and Properties of Soils), NC Brady has undoubtedly had a major impact on the development of Philippine soil science.

At UPLB, some of the soil scientists who represented, or were product of, the "golden age" and who became influential teachers included: R.B. Badayos (genesis, survey and classification); I.J. Manguiat  and E.S. Paterno (soil microbiology); G.O. San Valentin (soil mineralogy and soil chemistry); A. A. Briones (soil physics) and E.P. Paningbatan (soil physics and soil conservation); A.M. Briones, D.A. Carandang (soil chemistry); and C. P. Mamaril, H.P. Samonte, W.C. Cosico (soil fertility). Two foreigners also spent a few years teaching soil science at UPLB: Dr. S. Srinilta (soil physics) and Dr. U. Jones (soil fertility).

A special mention must be made of Nicolas L. Galvez, a highly trained and outstanding soil scientist who took charge of developing the Soils Department and of training future Filipino soil scientists at UPCA after the war. N.L. Galvez was the head of the Soils Department from 1948 to 1961 and served UPCA for 42 years. Without doubt, Dr. Galvez had the greatest contribution to Philippine soil science. For this reason, he is widely considered as the "Dean of Filipino Soil Scientists". (A museum has recently been established in his honor at UPLB).

Outside UPLB, examples of soil scientists who also stood out during the 1980s and 1990s were J.B. Dacayo of Central Luzon State University (CLSU), S.S. Magat of Philippine Coconut Authority, R.G. Escalada of VSU who advised more than a hundred undergraduate thesis students in agronomy and soil science (including this writer), and N.B. Inciong of BSWM.

At present, there is a new generation of well-trained soil scientists, many of whom have obtained advanced degrees from prestigious universities in Australia, Japan, Europe, and North America, who are working at various universities, research centers, government agencies, and private organizations throughout the country. Undergraduate/graduate degree programs in soil science are now offered by several universities throughout the country the most important of which are UPLB, CLSU, Benguet State University, Tarlac Agricultural University, and Central Bicol State University of Agriculture in Luzon; Visayas State University or VSU (formerly called ViSCA and LSU) in central Philippines; and University of Southern Mindanao and Central Mindanao University in the southern part of the country. Survey, mapping, and soil fertility evaluation of soils throughout the country are carried out by the Bureau of Soil and Water Management based in Quezon City.

The soil science program at VSU in Baybay, Leyte, deserves a brief mention. Started in the late 1970s, the program has produced graduates who are now successful academics and scientists not only in the Philippines but also in the USA, Europe and Japan. VSU soil scientists have also produced high quality papers which have been published in various international journals. On November 5, 2014, the VSU administration under President Jose L. Bacusmo created the Department of Soil Science from the existing Department of Agronomy and Soil Science. In terms of faculty strength, facilities, and scientific publication, VSU's Department of Soil Science is widely considered as the country's leading soil science department at the moment.*

Finally, Philippine soil science has clearly made major strides in the last three decades but it lags very much behind those in other countries in terms of scientific outputs and professional activities. This is even true for the ASEAN region alone. Regarding scientific outputs, very few papers have been published by Filipino soil scientists in peer-reviewed international journals. In terms of professional activities, the Philippine Society of Soil Science and Technology (PSSST) has not yet been fully recognized by the International Union of Soil Sciences, the global organization of soil scientists. So it cannot be seen in the global map of soil science. There is an increasingly popular view among young soil scientists that basing the PSSST at the BSWM, a non-academic entity, has stifled the development of the organization and of soil science in the country.
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* The two soil scientists (V.B. Asio & I.A. Navarrete) included in the top 450 scientists in the Philippines in 2016 based on scientific citations & h index by Webometrics (http://www.webometrics.info/en/node/148) are from the Department of Soil Science of VSU.


(Note: The article is based on the available historical materials that I have gathered so far. I will revise it when new information becomes available.)

Heavy metal pollution and nutrient deficiency problems in the abandoned Bagacay mine in Samar island

The National Policy Agenda on the Revitalization of Mining in the Philippines in 2004 gives top priority to the remediation and rehabilitation of abandoned mining sites all over the country. Consequently, the Department of Environment and Natural Resources (DENR) has identified remediation and rehabilitation of several abandoned mining sites as one of its top priorities (MGB-MESD 2006). Among all abandoned mining sites throughout the country needing urgent rehabilitation, the Bagacay Mine ranks first (MGB-MESD 2006).

Bagacay Mine, located at the border of a nature reserve in the western part of Samar Island, was formerly worked for the recovery of pyrite (FeS2) and copper (Cu) for nearly 50 years until its abandonment in 1992. It exhibits many environmental problems such as heavy metal pollution of soil and water and the formation of Acid Mine Drainage. Recent efforts to rehabilitate the area by re-vegetating it with introduced trees species such as mahogany (Swietenia macrophylla), mangium (Acacia mangium) and ipil-ipil (Leucaena leucocephala) as well as some grass species like tiger grass (Thysanolaena maxima) were a total failure.

An environmental assessment by the Mines and Geosciences Bureau (MGB-MESD, 2006) revealed very high levels of heavy metals in sediments (and soils) collected from various parts of the abandoned mining site. For the upstream sediments (soil and sediments deposited by various tributaries unaffected by mining activities), the levels of heavy metals (in mg/kg) were: Fe (5,900 to 96,000), Cu (9 to 2,216), Zn (<1 to 516) and Pb (22 to 694). The midstream materials which included rock and soil materials from the main pit and waste dumps, silt and sediments in the pit, and tailings from the tailing dams were more polluted and showed the following concentrations (mg/kg): Fe (36,400 to 487,500), Cu (220 to 50,100), Zn (100 to 187,700), Pb (8 to 2,341), As (6 to 5,969) and Hg (1 to 13). For the downstream sediments (from the Taft River), the heavy metals concentrations in mg/kg were: Fe (104,300 to 373,500), Cu (466 to 5,279), Zn (2,314 to 7,138), Pb (44 to 354), As (352 to 693) and Hg (2 to 5).

Some native plant species are starting to grow in clumps even in the most polluted portions of the abandoned site. Edralin (2008) collected soil samples around each clump of the native plants as well as plant tissues for chemical analysis. Findings revealed that the soil in the spots where the plants are starting to grow still have very low fertility status and are extremely acidic aside from containing excessive levels of the heavy metals. The study showed that the native plants that start to grow in the area have low nutrient (N and P) requirement and are able to tolerate the polluted condition either by not absorbing (avoiding) the heavy metals or by absorbing high levels of the metals (the study considered only Cu and Pb). The concentration of Cu in the plants such as Saccharum spontaneum L. and Neonauclea formicaria (Elm.) Merr. was positively correlated with the soil OM content. Two fern species Pityrogramma calomelanos (L.) Link and Lycopodium cernuum L. showed the highest concentrations of Cu in their tissues with values that fall within the toxic range for plants. Also, the highest concentration of Pb was shown by Lycopodium cernuun L. and Dicranopteris linearis (Burm.) Underw. with some of their Pb values also falling within the plant toxicity range.

References

Doyle C, Wicks C, Frank N 2007. Mining in the Philippines Concerns and Conflicts. Fact Finding Mission to the Philippines Report. Society of St. Columban, Widney Manor Rd., Knowle, Solihull B93 9AM, West Midlands, UK

Edralin Don Immanuel A. 2008. Copper, lead, nitrogen and phosphorus levels in soils and plants in the abandoned Bagacay mine in Western Samar. MSc thesis in tropical ecology, Visayas State University, Baybay, Leyte, Philippines.

Kabata-Pendias A 2004. Soil-plant transfers of trace element- an environmental issue.
Geoderma 122: 143-149

Mines and Geosciences Bureau - Mining Environment and Safety Division (MGB-MESD) 2006). Environmental Assessment of Abandoned Bagacay Mine Relative to the Proposed Interim Remediation Measures of the World Bank Supported Project. North Avenue, Diliman, Quezon City.

Is soil science in an upswing?

In many countries, soil science has been traditionally associated with agriculture because of the major function of soil as a medium for plant growth. So it was no surprise that the decline in funding for agricultural research worldwide in the last two decades had taken its toll on student enrolment in agricultural sciences including soil science. But there are good signs that soil science is now experiencing an upswing particularly because of its strong link to environmental management and global warming (soil is a major source and sink of carbon) and to recent increased focus on agriculture.

In a recent paper published in Geoderma, Dr. Alfred E. Hartemink of ISRIC in Wageningen, Netherlands, and Prof. Alex McBratney (University of Sydney) think that soil science renaissance (from French word meaning "rebirth") is currentyl taking place "where novel approaches to thought are combined with a revival of ideas from the past." They noted that renewed interest in food, feed, and fuel production and the publication of numerous reports have brought soils back onto the global research agenda.

Recent reports by the United Nations and other international organizations have highlighted the need for up-to-date and fine resolution soil information and the revival of soil research. They cited as examples of key issues that have been discussed in recent publications soil erosion, nutrient depletion, and pollution particularly in relation to environmental degradation, climate change, and world food production. They estimated that about 3.2 billion euro is spent yearly on soil research worldwide. They urge the soil science community to benefit from the current upsurge in soil science.

Reference

Hartemink AE and A McBratney. 2008. A soil science renaissance. Geoderma 148: 123-129.

Effects of biosolids application on N mineralization

Sewage sludge is the solid, semi-solid or liquid residue generated during the treatment of domestic sewage. Biosolids are the treated form of sewage sludge. The use of biosolids as soil amendments is widely seen as a way to reduce the accumulation of wastes and at the same time to enhance soil fertility for crop production. Studies have shown that the use of biosolids as soil amendment is an effective means of recovering plant nutrients and improving the physical and microbiological properties of soils.

However, there are problems associated with the use of biosolids such as heavy metal contamination and nitrate pollution. Biosolids containing excessive levels of heavy metals should not be used as soil amendments. As for nitrate pollution due to excessive mineralization, Hseu and Huang (2005) proposed that this maybe avoided by regulating the annual rate of application of biosolids to soil based on crop N requirement and the anticipated net amount of organic N mineralized in the soil treated with biosolids.

In an interesting study aimed to characterize the influence of the application of biosolids on the soil potential for N mineralization (N0) and also to elucidate the kinetics of N mineralization in tropical soils treated with different biosolids, Hseu and Huang (2005) used anaerobic biosolids and aerobic biosolids obtained from the wastewater treatment plants in Kaohsiung and Taipei, Taiwan. The biosolids were applied at rates of 10, 50 and 100 Mg ha−1 to three tropical soils and incubated for 48 weeks.

Findings of the study revealed that addition of both kinds of biosolids to the soil increased N mineralization potential to an extent related directly to the application rate and the N content of the biosolids. However, the cumulative amounts of N mineralized for soil treated with aerobic biosolids greatly exceeded those for the soil treated with anaerobic biosolids. Sandy soil treated with biosolids exhibited a relatively low potential for mineralizing N.

The contamination of the biosolids with relatively high levels of heavy metals such as Cu and Zn did not prevent an increase in N mineralization resulting from the application of biosolids to the soils. Approximately 3–34% of the total N content in the biosolids-treated soils was mineralized for 48-week incubation. Based on a demand of 150 kg N ha−1 for vegetable production in Taiwanese soils, the rate of biosolids application in the three soils are safe and will not cause nitrate accumulation.

Reference

Hseu ZY and CC Huang. 2005. Nitrogen mineralization potentials in three tropical soils treated with biosolids. Chemosphere 59: 447-454.

Could the alkaline soils of the world be the missing carbon sink?

The missing carbon sink is the large amount of unidentified carbon sink in the global carbon budget. According to the Woods Hole Research Center (2007) the average annual carbon emissions amount to 8.5 Pg (1 Pg or petagram is equal to 1 billion metric tonnes) comprising of 6.3 Pg from combustion of fossil fuels and 2.2 Pg from changes in land use. This is greater than the sum of the annual accumulation of carbon in the atmosphere (3.2 Pg) plus the annual uptake by the oceans (2.4 Pg) which is only 5.6 Pg. The difference of 2.9 Pg (i.e. 8.5-5.6=2.9) is unknown carbon sink required to balance the carbon budget.

Scientists have been searching for this big amount of unknown carbon sink during the last two decades. It was first thought to be located in the ocean considering that it occupies 70% of the earth’s surface. However, most scientists consider that the ocean sink is not big enough to account for the missing carbon (Xie et al., 2009). The next possible location is the world’s forest. In fact, many scientists believe that this large amount of missing carbon is absorbed by land-based carbon sinks particularly forests but estimates indicate that terrestrial ecosystems are a net sink of only 0.7 billion (Woods Hole Research Center, 2007). Some studies have revealed that carbon accumulation is largely counterbalanced by carbon loss from deforestation.

In a study published in Science, an international team of scientists led by Stephens (Stephens et al., 2007) revealed that the missing link may indeed be located in tropical ecosystems. They reported that northern terrestrial uptake of industrial carbon dioxide emissions is smaller than previously thought and that, after subtracting land-use emissions, tropical ecosystems may currently be strong sinks for carbon dioxide. But whether or not this is enough to account for the missing carbon is not yet clear.

The third possible location of the missing carbon sink is the soil which is one of the largest dynamic carbon pools on earth. In a recent paper published in the journal Environmental Geology, researchers from China revealed a carbon sink which has been largely overlooked in the past. Xie et al. (2009) reported that alkaline soils (i.e. soils with pH > 7.0) on land are absorbing CO2 at a rate of 0.3-3.0 μmol m-2 s-1 with an inorganic, non-biological process. The intensity of this CO2 absorption is determined by the salinity, alkalinity, temperature and water content of the saline/alkaline soils. They estimated the range at 62-622 g C m-2 year-1. Considering that there are about 700 million hectares of alkaline soils around the world, the amount of CO2 absorption could be very significant on a global scale and could be a major part of the missing carbon sink.

References

Woods Hole Research Center. 2007. The missing carbon sink. http://www.whrc(carbon/missingc.htm

Stephens B.B. et al. 2007. Weak northern and strong tropical land carbon uptake from vertical profile of atmospheric CO2. Science 316: 1732-1735.

Xie J, Y Li, C Zhai, C Li and Z Lan. 2009. CO2 absorption by alkaline soils and its implication to the global carbon cycle. Environmental Geology 56: 953-961.

Native tree species affect changes in chemical properties of a highly weathered soil

Contributed by Juvia P. Sueta, University of Göttingen, Germany

There is growing interest in the use of indigenous tree species in reforestation programs at present. Thought to be well adapted to their native areas, indigenous tree species are able to survive well and strongly influence the soil. However, the lack of published data on their performance often limits their full use and casts uncertainties on whether they have beneficial or negative impacts on the soil. To better understand the role of trees in improving soil quality, an understanding of how nutrient availability changes with time is important (Kelly and Mays, 1999).

In this study which we conducted at the VSU-GTZ reforestation project site (see photo) in Mt. Pangasugan, Leyte, Philippines, we looked at the influence of two native tree species- Parashorea plicata and Dipterocarpus warburgii- on the nature and rate of changes on the chemical properties of a highly weathered soil following a change in land use from Imperata grassland to plantation of indigenous tree species. Monthly sampling of carefully selected plots in two sites (dominated by native or indigenous species) was carried out to evaluate temporal as well as spatial variations in important soil chemical properties. In addition, rates of litter decomposition of the two species were also investigated on the sites.

We found significant monthly variations of soil pH, organic matter content, total N and available P. Significant differences between sites were also observed for organic matter, total N as well as Ca and Mg contents suggesting individual tree species effects. For most of the soil properties evaluated, irregular fluctuations at certain times of the year characterized by periods of high and low availability. This suggests a highly dynamic nutrient cycling within the system.

The influence of these native tree species could be attributed to its litter contribution to the soil. In both sites, some centimeters thick of organic layer could be observed on the soil surface throughout the year. An evaluation of decomposition revealed high rates for both species. This result suggests that aside from being dynamic, the cycling of nutrients also tends to be efficient. This efficient cycling of nutrient may also help explain why these native tree species appeared to grow well despite the inherently low levels of nutrients in this old, highly weathered soil.

References

Kelly JM and PA Mays. 1999. Nutrient supply changes within a growing season in two deciduous forest soils. Soil Sci Soc Am J 63: 226-232.

Sueta JP, VB Asio and AB Tulin. 2007. Chemical dynamics of a highly weathered soil under indigenous tree species in Mt. Pangasugan. Annals of Tropical Research 29: 73-89.