In this study we have shown that feed backs are significant in both directions and have also shown that money and exchange rate shocks affect prices. Thus, any reduction in government expenditure in agriculture affects the path by which price shocks feedback on money and the exchange rate. From a policy perspective, this is very important, since it implies that any change in government support of the farm sector should be evaluated from an integrated market point of view. This more integrated or global perspective is needed because expenditures and budget deficits, monetary, exchange rate, and farm policies are significantly related and their interactions far too strong to be neglected. Triclosan is a non-agricultural pesticide widely used as an antibacterial agent in common medical, household and personal care products in the range of 0.1%–0.3% . The use of TCS has increased worldwide over the last 30 years . The broad household use of products containing TCS results in the discharge of TCS to municipal wastewater treatment plants, and it has been detected in effluents and sewage sludge in Europe and the United States .The mode of action of TCS on bacteria is through inhibition of fatty acid synthesis by targeting enzymes specific to bacteria . Since fatty acid biosynthesis is a fundamental process for cell growth and function; the ability to inhibit this makes TCS a particularly effective antimicrobial compound. Bio-solids are the nutrient-rich byproduct of wastewater treatment operations and large quantities are generated. For example, approximately 750,000 dry tons is produced annually in California and 54% of these bio-solids are applied on agricultural lands, 16% are composted and the remaining 30% goes to landfills . Concerns about potential health and environmental effects of land application of bio-solids include possible off-site transport of pathogens, heavy metals,growing raspberries in containers and trace organic constituents such as TCS . A less explored set of potential impacts is how TCS and other bio solid-borne contaminants affect ecosystem processes and associated soil microbial communities.

Potential impacts on soil microorganisms are important to assess since these organisms mediate much of the nitrogen, carbon and phosphorous dynamics in soil, biodegrade contaminants, create soil structure, decompose organic compounds, and play a major role in soil organic matter formation . We hypothesized that bio-solids containing TCS would have detrimental effects on soil microbial communities by decreasing biomass and altering community composition in agricultural soil. Our objectives were to evaluate the effects of increasing amounts of TCS on soil microbial community composition in the presence and absence of bio-solids. We used phospholipid fatty acid analysis to characterize the response of microbial communities; the method provides information about microbial community composition, biomass, and diversity . Experiments in which TCS was added to soil without bio-solids allowed the relative effects of bio-solid and TCS addition on microbial community composition and function to be compared and also provided a “secondary control” because TCS-free municipal bio-solids are essentially unavailable in the United States . Triclosan was purchased from Fluka . Yolo silt loam was collected from the Student Experimental Farm at the University of California, Davis at a depth of 0 to 15 cm. The soil was passed through a 2 mm sieve and stored at 4 °C until use. Bio-solids originated from a municipal wastewater treatment plant in Southern California that employed a conventional activated sludge treatment system followed by aerobic sludge digestion. Bio-solids from this system were selected for study because they had the lowest concentration of TCS among those collected from 10 different wastewater treatment plants in California . The soil and bio-solid physiochemical properties are reported in Table 1 and were determined using standard techniques . The soils were moistened to 40% water-holding capacity, which is equivalent to 18% water content in our experiments, and pre-incubated for 7 days at 25°C to allow time for normal microbial activity to recover to a constant level after disturbance. The pre-incubated 50 g of soil was weighed into 200 ml glass bottles to make three replicates per treatment. For the bio-solid amended soil sample, 20 mg/g of bio-solid was added. Each treatment sample was then spiked with TCS to achieve final concentrations of 10 or 50 mg/kg using TCS stock solutions prepared in acetone, as recommended by Waller and KooKana .

This spiking level was chosen as a conservative upper bound on anticipated soil concentrations in the field. The lower spiking level is below the mean concentration observed in US bio-solids and the higher level is below the 95th percentile for US bio-solids ; adding bio-solids to soils at typical application rates would produce soil concentrations ~50–200 times lower. Control samples were also prepared with acetone only. After that, the solvent was allowed to evaporate inside the fume hood before the samples were thoroughly mixed. The microcosms were incubated in the dark at 25°C for 0, 7 and 30 days. Every week, each vial was opened to help keep conditions aerobic and the water content of each set of samples was measured and water was added as needed to maintain target moisture levels. At each sampling time, the remaining TCS was measured by drying 3–5 g samples at 70°C for 24 hours and homogenizing with a mortar and pestle. Replicate 1 g subsamples of each dried sample were placed in centrifuge tubes, spiked with deuterated trichlorocarban in methanol, air dried under a fume hood to remove the methanol, and then mixed well. Extraction was performed by adding 15 mL of 1:1 acetone and methanol to the centrifuge tube. Samples were extracted on a shaker table for 24 hours at 295 rpm and 55 °C and then centrifuged for 30 min at 4,100 g. The supernatant was diluted as needed to ensure that the concentration remained within the linear portion of the calibration curve. The extracts were analyzed for TCS using LC-MS/MS. Additional details regarding the extraction and analysis procedures can be found in Ogunyoku & Young . Recoveries of deuterated TCC ranged from 63–115% during extraction and analysis.As expected, the bio-solids contained far larger amounts of nitrogen and carbon than the Yolo soil . Even though the bio-solids constituted less than 2% of the amended soil, they contributed nearly 50% of the total nitrogen and 40% of the total carbon in the amended soil system. The bio-solids contained an abundance of nutrients accumulated as by-products of sewage treatment in forms likely to be more labile than equivalent nutrients present in the soil. As will be discussed further, the greater availability of C and N in the SB than soil treatments had a strong influence on some of the results, especially at the early time points. In the following section, therefore, it is useful to remember that all SB treatments contain more available C and N than all soil treatments. The initial concentration of TCS in unspiked SB samples was very low ,large plastic pots for plants fell below the quantitation limit for TCS after 7 days, and was not detectable after 30 days of incubation. Significant TCS bio-degradation was observed in spiked soil and SB samples during incubation and the data were well described using a first order model as indicated by linear plots of ln against time . Degradation trends were consistent at the two spiking levels for each sample type but bio-solid addition significantly reduced degradation rates at both spiking levels compared with un-amended samples. The percentage of TCS removed was approximately two times greater in soil than in SB samples. Approximately 80% of the TCS was removed over 30 days in soil treated with either 10 mg/kg or 50 mg/kg of TCS, but no more than 30% was transformed in the corresponding SB microcosms.

The reduced bio-degradation in the SB microcosms may have resulted from the ~40% higher carbon content in the SB microcosms, which would be expected to increase the soil-water distribution coefficient by a comparable amount. Reduced TCS concentration in soil pore water would be expected to slow bio-transformation, potentially in a nonlinear fashion. Another possible contributor to the slower degradation of TCS in SB is the greater availability of alternative, likely more easily degradable, carbon sources in SB than soil microcosms, reducing the use of TCS as a substrate. Selective bio-degradation of one carbon source, and inhibition of the degradation of other chemicals also present, has been observed for mixtures of chemicals in aquifers . To assess which of these mechanisms was controlling, measured Freundlich isotherm parameters for TCS adsorption on bio-solid amended Yolo soil were used to calculate equilibrium pore water concentrations in the soil and SB microcosms over the course of the experiment. Using estimated pore water concentrations of moistened soil and SB samples, instead of total soil concentrations to perform half-life calculations, resulted in modest increases in the rate constants and decreases in half-lives of soil samples and did not narrow the significant gap between half lives in soil and SB . This suggests that the primary reason for the slower degradation of TCS in bio-solid amended soils is the increase in more labile forms of carbon because organic material is highly porous and has a lower particle density. Previous research shows that TCS biodegrades within weeks to months in aerobic soils , although Chenxi et al., found no TCS degradation in bio-solids stored under aerobic or anaerobic conditions, Kinney et al., observed a 40% decrease in TCS concentrations over a 4-month period following an agricultural bio-solids application. Because the slopes of the lines in Fig. 1 are not significantly different as a function of spiking level , the slopes were averaged for each treatment type, yielding apparent first order rate constants of 0.093±4% d−1 for soil samples and 0.024±41% d−1 for SB samples where the percent error represents the relative percent difference between the 10 mg/kg and 50 mg/kg degradation curves. These apparent rate constants translate to half-life estimates of 7.5 d in soils and 29 d in bio-solid amended soil. The estimated half-life of TCS in soil is within the range of previously reported half-lives of from 2.5 to 58 d in soil . The half-life determined here in bio-solid amended soils is lower than the one available literature value of 107.4 d . The microbial biomass decreased in the TCS spiked samples after 7 or 30 days of incubation in comparison with the unspiked controls, for both soil and SB, and the decline was statistically significant at 50 mg/kg . Although exposure to TCS caused declines in biomass in both soil and SB microcosms, the total microbial biomass was two times higher in SB than soil probably due to the increased availability of nutrients and/or possibly due to addition of bio-solid associated microorganisms in the latter . The total number of PLFAs ranged from 42–47 in soil and 48–59 in SB . No significant change in numbers of PLFAs was evident with increasing dosage of TCS for any incubation time suggesting that TCS addition did not adversely affect microbial diversity. Microbes respond to various stresses by modifying cell membranes, for example by transforming the cis double bond of 16:1ω7c to cy17:0, which is more stable and not easily metabolized by the bacteria, reducing the impact of environmental stressors . Consequently, the ratio of cy17 to its precursor has been employed as an indicator of microbial stress that has been associated with slow growth of microorganisms . Increases in this stress biomarker were observed in both soil and SB samples as TCS concentrations increased , suggesting that TCS has a negative effect on the growth of soil microorganisms. The overall level of cy17 to its precursor is lower in SB than soil samples, suggesting that nutrients contributed by the bio-solids reduce stress on the microbial community. Our study agreed with a previous study showed that carbon added to soil led to a reduction in the cy17 fatty acid TCS additions, however, increased the stress marker compared with that detected in the corresponding samples with no added TCS. A broader implication of this result is that presence of bio-solids may mitigate the toxic effects of chemicals in soil, or chemicals added in combination with bio-solids, on soil microbial communities. Groupings of microbial communities, based on CCA analysis of their composition as estimated by PLFA, were distinguished primarily by whether they were in soil or SB treatments and secondarily by time since spiking .