So now I need to completely rethink it, and I've had a few ideas. So far this seems the most motivating:

The effect of soil microbial populations on drought resistance of millet.

This is mostly important in context of the paper Ekundayo, EO, 2003. “Effect of common pesticides used in the Niger Delta basin of southern Nigeria on soil populations.” Env. Monit. Ass. 89: 35-41, which found that some pesticides impaired soil microbes. The Niger Delta is seriously affected by drought, and one of the main crops grown on the floodplains is millet. So if soil microbes help plants resist drought, use of said pesticides may be exacerbating drought effects. One land management solution would be to protect flood forests, which provide nesting sites for cattle egrets and other waterfowl. Cattle egrets eat insects, particularly locusts, so removal of cattle egret habitat is likely to increase crop damage by locusts, combatted by pesticide use, which then exacerbates drought. I think it's likely that soil microbes will make plants more resistant to drought by facilitating nutrient transport and thereby allowing increased growth and lower incidence of plant malnutrition etc. Better growth also means better root networks, which in turn means less soil erosion. Hence, rather important.

I think that sounds pretty good. So I'll be writing to my supervisor on Monday to see if it's feasible and if so finalise methods.

Anyone have any information regarding drought and soil microbes, or on the Niger Delta in general? I find the region fascinating.

Is the environmental cost of intensive livestock production too great?

• DEFRA website. Scope the site using the search facility and terms such as LINK, science, environment, sustainability and Policy Commission for the Future of Farming and Food.
• DEFRA LINK Sustainable Livestock Production
• Scottish Executive (2002). Prevention of Environmental Pollution from Agricultural Activity.
• Ostergaard V and Hansen JP (1995). Indicators - a method to describe the sustainability of livestock farming.
• Scottish Executive (2001). A forward strategy for Scottish Agriculture. [Annexe A gives financial information about the livestock sector].
• The SAC 4 Point Plan

1658/2000

Pollution of the biosphere: Emerging chemical contaminants: the case of perfluorochemicals. Summarise and discuss the extent of biospheric contamination and the risk to health from the use of these fully fluorinated organic compounds by industry and commerce.
 

Persistent organic pollutants (POPs) are those that have the capacity to be retained in the environment over long periods of time, often with high potential for long-distance transport and bioaccumulation. Most POPs, such as PCBs and DDT, have lipophilic properties whereby they bioaccumulate in fatty tissues, concentrations increasing exponentially to toxic levels in higher trophic levels. Thus bald eagles (top predators) have experienced eggshell thinning through toxicity of DDT, despite insufficient concentrations in primary consumers to produce adverse effects (EPA, 1978). In order to prevent damage to wildlife and human health, the Stockholm Convention on Persistent Organic Pollutants has attracted 151 signatories worldwide with the intent of reducing or eliminating their release into the environment (UNEP, 2005).

In 1976, Guy & Taves detected organic fluorine in human blood after the fluoridation of drinking water, provoking investigation into the fate of fluorochemicals in the environment. Previously, the most abundant fluorochemical of concern and an end-stage metabolite and environmental degradation product of other fluorochemicals (Schnellman, 1990; Olsen et al., 1999; Karrman, 2004; Xu et al., 2004), perfluorooctane sulfonate (C₈F₁₇SO₃^-, PFOS), was deemed safe because, unlike most POPs, due to its lipophobic properties it does not accumulate in fatty tissues, and it does not react with DNA (EPA, 2000a). However, bioconcentration factors have been calculated at 10-20 for North American bald eagle and mink tissue, and approximately 1000 in benthic invertebrates, relative to their prey species (Kannan et al., 2005), and following accidental spillage of fire-retardant foam containing fluorinated surfactants, leading to contamination of Etobicoke Creek in Canada, bioconcentration factors of 6300-125000 were found in fish liver tissue relative to surface water (Moody et al., 2002). 

PFOS and the related perfluorochemical PFOA (perfluorooctanoic acid, a peroxisome proliferator – Kennedy et al., 2004) to a lesser degree tend to accumulate in the liver, kidneys, gall bladder and blood (perhaps recognised by the body as a bile acid, which is then recycled into the liver – Van den Heuvel et al., 1991; Kannan et al., 2002a; Kannan et al., 2002b; Jones et al., 2003), and impair gap junction intercellular communication, which is important for normal cell growth and function (Hu et al., 2002).

Previously, it was also assumed that PFOS would pose a lesser risk because it is relatively involatile, so should have low potential for long-range transport. However, it has been shown that PFOS an PFOA are degradation products (primarily via biological transformation in aquatic systems) of other more volatile and thus further-transported perfluorochemicals such as perfluoroalkyl sulfonamides (PFASs) (Shoeib et al., 2004; Dinglasan et al., 2004; Dimitrov et al., 2004), which would explain the worldwide detection of PFOS in oceanic water, and blood and tissue samples.

Kannan et al. (2002c) found PFOS present in the livers 100% of river otters sampled in Washington and Oregon, USA, and it is generally found at biomagnified concentrations at higher trophic levels, e.g. mink, otters, bald eagles, despite relatively low concentrations in fatty deposits (Giesy & Kannan, 2001). Higher levels of PFOS detected in liver and kidneys of stranded marine organisms of the North Sea further indicate biomagnification (Van de Vijver et al., 2003).

High residence time supports the theory that PFOS will persist in the environment (Giesy et al., 2001; Moody et al., 2002; Moody et al., 2003), and low levels have already been detected in animals in remote locations, e.g. 100% of a sample of Arctic species analysed in a 2004 investigation (Tomy et al., 2004; Martin et al., 2004a), indicating a potential for long-range transport, although at lower concentrations than closer to the source, e.g. the Great Lakes, Baltic and Mediterranean Seas (Giesy & Kannan, 2001; Martin et al., 2004b), downstream of the industrialised Pearl River Delta in southern China (So et al., 2004), and in Tokyo Bay (Taniyasu et al., 2004). Our contamination may have been even more extensive than planet Earth, due to the use of perfluorinated membranes manufactured by DuPont in fuel cells for space travel (Banerjee & Curtin, 2004).

In 2002, there was a class action suit against DuPont (also makers of the popular non-stick material Teflon®) after a farmer’s cows close to a landfill wasted and died, and it was found that drinking water had been contaminated (despite an appallingly unethical attempted cover-up by DuPont and West Virginia Department of Environmental Protection – Leach et al. v. DuPont and Lubeck Public Service District, 2002). Inhabitants near the PFOA-manufacturing plant were found to have a 12fold increase in blood serum concentrations compared to background levels (EWG, 2004), and a local newspaper reported respiratory difficulties and developmental problems in humans, and an observed increase in wildlife mortality (Lyons, 2003). Employees of one of 3M’s perfluorooctanesulfonyl fluoride manufacturing plant in Alabama, USA, who would have been exposed to a greater level of contamination than the background population, experienced benign colon polyps, malignant colorectal tumours and malignant melanoma (Olsen et al., 2004).

Indeed, dust samples of all the Japanese homes in a 2003 study contained PFOS and PFOA at low levels (Moriwaki et al., 2003), and PFOS was found in blood serum of all non-occupationally exposed human volunteers tested by both an American and a Canadian team, with all American volunteers also testing positive for PFOA, perfluorohexanosulphate (PFHxS), and perfluorononanoate (PFNA) and nine out of thirteen fluorochemicals in at least 75% of subjects (Kuklenyik et al., 2004; Kubwabo et al., 2004). Even Inuit of Nunavut, Northern Canada, were found to have traces of fluorinated organic compounds in their blood plasma (Tittlemier et al., 2004). Male humans tend to accumulate PFOA in their tissues quicker than females, although the levels are essentially equivalent after the age of about 60 (Harada et al., 2005). Kuklenyik’s investigation on American subjects could easily be applied to a wider sample of volunteers, providing a better indication of the global levels of perfluorochemical contamination in humans, and monitor their rate of change over time.

PFOA is the second most abundant fluorinated compound found in humans (Gilliland & Mandel, 1996; Kannan et al., 2004), and has been associated with increased occupational exposure leading to increased bladder cancer mortality (Alexander, et al., 2003) and a more than threefold increase in prostate cancer mortality (Gilliland & Mandel, 1993). Adverse effects on wildlife have also been shown in laboratory experiments with perfluorochemicals. Zooplankton and northern leopard frog population survival was seen to decrease by 90-100% in two weeks upon exposure to 10mg/L PFOS (Sanderson et al., 2002; Ankley et al., 2004). Postnatal mortality was observed in rats (Grasty, et al., 2002; Lau et al., 2001). Increased mortality and significant adverse effects were observed in monkeys when exposed to low levels (0.75mg/kg/day) of PFOS for 182 days, including weight loss, increased liver weight, reduced serum cholesterol, and reduced reproductive and thyroid enzymes (Seacat et al., 2002). PFOA is also a definite hepatocellular carcinoma promoter in rodents at a concentration of 0.02% of the basal diet (Abdellatif et al., 2003-2004).

Current ambient levels of PFOS and PFOA are lower by at least a factor of two than the level required to observe adverse effects in zooplankton and the midge Chironomus tentans (sensitive biotic indicators - Boudreau et al., 2003; MacDonald et al., 2004), but because the compounds are persistent and continue to be leached into the environment from landfills and public water disposal sites, e.g. the Kinki region of Japan (Harada et al., 2004; Saito et al., 2004), and continued industrial and commercial use of fluorinated compounds (4,481 metric tons globally in 2000 – OECD, 2002), e.g. in McDonalds packaging (EWG, 2004), their environmental concentrations can be expected to increase. Furthermore, the outdoor environmental concentrations of perfluorochemicals tend to considerably lower than those indoors (Shoeib et al., 2004). An increasing tendency for citizens of industrialized countries to spend more time indoors, with the age of information and consumerism, also means we subject ourselves to higher levels of exposure. Exposure in these cases could be lessened somewhat by reducing the proportion of carpeted floors in the home (Kubwabo et al., 2005), and not using non-stick pans or use food cartons with non-stick coatings, because perfluoro additives migrate from the cookware or food cartons to cooking oil by a factor of mgkg^-1 (Begley et al., 2005).

Ideally, of course, perfluorochemicals will become obsolete, having been replaced by compounds of similar utility but lower environmental impact. One example of a class of compounds that is being studied is hydrofluoropolyethers as flame-retardants (Malinverno et al., 2005). A couple of interesting development are the discovery that sonochemical decomposition of PFOS and PFOA yields shorter-chain polymers with decreased half-life (Moriwaki et al., 2005), and that a persulfate can be used as a photochemical oxidant to increase the decomposition rate of PFOA (Hori et al., 2005). These methods could in theory be used in waste disposal of PFOS and PFOA, lessening the impact of landfills and public water disposal sites.

However, so too seem the “safe levels” assigned to drinking water to increase sporadically, in Ohio by a factor of 150 (from 1ppb to 150ppb - OEPA, 2002). Regardless, the possibility of accidental spillage e.g. contamination of Etobicoke Creek, Canada, as well as deliberate concentrated use e.g. of fire-fighting foam in Tomakomai, Japan (Yamashita et al., 2004), raising environmental concentrations remains a real concern (Moody et al., 2002; Oakes et al., 2004). On the other hand, these concentrations may end up being almost entirely arbitrary, given that effects on cell membranes (facilitating contamination by all pollutants) are seen well below the levels associated with other adverse effects (Hu et al., 2003).

PFOS and the potentially hundreds of precursors and structural isomers (Langlois & Oehme, 2004) were under review to be added to the Stockholm Convention list in December 2005 (POPRC, 2006), and many manufacturers have endeavoured to voluntarily phase out PFOS-containing products, such as 3M’s Scotchgard (EPA, 2000b). However, the molecularly similar perfluorinated carboxylic acids and volatile telomer alcohols that degrade into PFOA are still used commercially as stain and water-repellents to treat textiles (Arsenault et al., 2004; Berger et al., 2004).

References:

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