Simazine Dissipation Research Articles

Improving Soil Simazine Dissipation Through an Organic Amendment Inoculated with Trametes versicolor

The aim of this research was to investigate the effect of applying sewage sludge combined with wheat crop residue as an organic amendment on the dissipation rate of simazine spiked at 2 and 20 mg kg−1 in an Andisol soil from southern Chile. Changes in some soil enzymes related to soil quality were measured by spectrophotometry, simazine dissipation rates were measured by gas chromatography, and biomass production in the contaminated soil was evaluated. Results of this study indicated that application of the organic amendment inoculated with Trametes versicolor enabled a decrease in negative effects of the herbicide on soil enzymatic activities and a reduction in final concentrations of simazine (~ 80% at both doses). The simazine half-life time was reduced from 14 to 10 days and from 36 to 15 days for doses of 2 and 20 mg kg−1, respectively. These findings prove that the combined strategy of biostimulation and bioaugmentation using these residues can be effectively used to reduce residue pesticides in soils, mainly by increasing the microbiological activity, thus improving simazine dissipation in an Andisol soil.

Influence of organic matter, nutrients, and cyclodextrin on microbial and chemical herbicide and degradate dissipation in subsurface sediment slurries

Pesticides leaching from soil to surface and groundwater are a global threat for drinking water safety, as no cleaning methods occur for groundwater environment. We examined whether peat, compost-peat-sand (CPS) mixture, NH4NO3, NH4NO3 with sodium citrate (Na-citrate), and the surfactant methyl-β-cyclodextrin additions enhance atrazine, simazine, hexazinone, dichlobenil, and the degradate 2,6-dichlorobenzamide (BAM) dissipations in sediment slurries under aerobic and anaerobic conditions, with sterilized controls. The vadose zone sediment cores were drilled from a depth of 11.3–14.6m in an herbicide-contaminated groundwater area. The peat and CPS enhanced chemical atrazine and simazine dissipation, and the peat enhanced chemical hexazinone dissipation, all oxygen-independently. Dichlobenil dissipated under all conditions, while BAM dissipation was fairly slow and half-lives could not be calculated. The chemical dissipation rates could be associated with the chemical structures and properties of the herbicides, and additive compositions, not with pH. Microbial atrazine degradation was only observed in the Pseudomonas sp. ADP amended slurries, although the sediment slurries were known to contain atrazine-degrading microorganisms. The bioavailability of atrazine in the water phase seemed to be limited, which could be due to complex formation with organic and inorganic colloids. Atrazine degradation by indigenous microbes could not be stimulated by the surfactant methyl-β-cyclodextrin, or by the additives NH4NO3 and NH4NO3 with Na-citrate, although the nitrogen additives increased microbial growth.

Simazine biodegradation and community structures of ammonia-oxidizing microorganisms in bioaugmented soil: impact of ammonia and nitrate nitrogen sources

The objective of the present study was to investigate the impact of ammonia and nitrate nitrogen sources on simazine biodegradation by Arthrobacter sp. strain SD1 and the community structures of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in non-agricultural soil. Soil microcosms with different treatments were constructed for herbicide biodegradation test. The relative abundance of the strain SD1 and the structures of AOA and AOB communities were assessed using quantitative PCR (q-PCR) and terminal restriction fragment length polymorphism (TRFLP), respectively. The co-existence of two inorganic nitrogen sources (ammonia and nitrate) had certain impact on simazine dissipation by the strain SD1. Bioaugmentation could induce a shift in the community structures of both AOA and AOB, but AOA were more responsive. Nitrogen application had significant impacts on AOA and AOB communities in bioaugmented soils. Moreover, in non-bioaugmented soil, the community structure of AOA, instead of AOB, could be quickly recovered after herbicide application. This study could add some new insights towards the impacts of nitrogen sources on s-triazine bioremediation and ammonia-oxidizing microorganisms in soil ecosystem.

Effects of Long-Term Use on Simazine Dissipation in Central California Vineyards

Simazine is an important management tool for weed control in vineyards because of its relatively low price, reliable control of several problem weeds, and long residual activity. After repeated and extensive use of simazine, several growers in the Central Valley of California expressed concerns about reduced, residual weed control with this herbicide. Experiments were conducted to evaluate the rate of simazine dissipation in soils with differing simazine-use histories and to determine whether residual weed control differed among sites. Two raisin vineyards were used in all studies, one with extensive simazine-use history (adapted) and one with no recent simazine-use history (nonadapted). Results indicated that simazine dissipation from biotic processes was fourfold greater in soil with a long simazine-use history relative to soil with no recent simazine applications. In the field, simazine persisted longer at the nonadapted site, and weed-control duration was affected by dissipation rate. Central Valley vineyard soils that have had repeated simazine applications can develop enhanced, microbial degradation, and reduced, residual weed control is possible; however, weed control is also affected by environmental conditions and other crop management practices.

Assessing Simazine Degradation Patterns in California Citrus Orchards with Different Simazine Use Histories

Simazine is commonly used to control broadleaf weeds and annual grasses in perennial tree and vine crops because of its relatively low cost and long residual activity. Simazine may be subject to enhanced biodegradation in some areas which can result in decreased herbicide persistence and reduced residual weed control. Laboratory studies were conducted to determine if rapid simazine degradation occurs in California citrus orchards and if degradation rates are correlated with simazine use history. In the Central Valley, simazine degradation curves indicate that simazine degradation rate is more rapid in soils with a simazine use history (adapted) compared to soils with no recent use (non-adapted). In these soils, simazine dissipation was two- to three-fold faster in adapted compared with the non-adapted soils. However, in southern California, simazine dissipation and mineralization were not substantially different among soils with different simazine use histories. Repeated simazine use in California orchards can lead to the development of enhanced microbial degradation of the herbicide. However, soil type and long-term cropping factors can affect persistence and distribution of herbicide-degrading microbial populations in California orchards.

Influence of Soil Properties on Bioaccumulation of 14C-Simazine in Earthworms Eisenia foetida

The toxicity of pesticides has been evaluated by several methods including tests with earthworms in both artificial and natural soils treated with the compounds. The ecological niches of earthworms make them good bioindicators of soil contamination. The bioaccumulation of 14C-simazine (6-chloro-N 2 -N 4 -diethyl- 1,3,5-triazine-2,4-diamine) was evaluated in earthworms (Eisenia foetida) maintained during three months in two substrates with different physical-chemical characteristics. The substrates were treated with 3.0 mg and 330 kBq of 14C-simazine kg−1 substrate. Results indicated that worms did not influence simazine dissipation in both substrates as indicated by similar recoveries and with no statistical differences with and without earthworms. The radiocarbon recoveries were 86.8 and 95.3%, respectively in the substrates with lower and higher organic matter contents with earthworms, and 91.0 and 107.4% in the same substrates without worms. However, in earthworms the recoveries were statistically higher when they were maintained in the substrate with lower amount of organic matter (0.89%) than from the higher one (0.33%). Consequently, 14C-simazine bioconcentration factor (BCF) was also greater in the substrate with lower organic matter (6.89 ± 1.55) than in the substrate with higher organic matter content (0.88 ± 0.06). The results suggest that the higher soil organic matter content will cause lower probability of contamination of soil organisms with simazine.

Ação de minhocas Eisenia foetida sobre a dissipação dos herbicidas simazina e paraquat aplicados no solo

Geralmente, os herbicidas são aplicados diretamente no solo, razão pela qual entram em contato direto com organismos deste ambiente, dentre eles as minhocas, as quais pelo metabolismo podem agir sobre resíduos desses compostos. Tomando minhocas da espécie Eisenia foetida como exemplo, determinaram-se a dissipação dos 14C-herbicidas (simazina e paraquat) e a bioacumulação destes compostos em seus tecidos, a partir de solo tratado com as concentrações recomendadas e, no caso do paraquat, também com concentrações superiores. Solo e minhocas foram analisados por extração com solventes e técnicas radiométricas, após 30 ou 90 dias de contato. As minhocas alteraram a dissipação do simazina, visto que houve 100 % de recuperação do radiocarbono na ausência de minhocas e 90 % na presença dos animais. Além disso, elas acumularam resíduos e, ou, metabólitos de simazina em seus tecidos, tendo-se detectado Fator de Bioacumulação (FB) de 1,45 e 1,17 após exposição ao solo tratado durante 30 e 90 dias, respectivamente. Por outro lado, a presença de minhocas não alterou o comportamento do herbicida paraquat aplicado ao solo, mas houve bioacumulação crescente de seus resíduos e, ou, metabólitos com o aumento da dose de tratamento (FB de 0,5; 3,2 e 5,5, respectivamente, nas concentrações recomendadas, 10 e 100 vezes superior).

Hexazinone and simazine dissipation in forestry field nurseries

Hexazinone and simazine field dissipation was studied in two different soils from Spain (Toledo and Burgos), devoted to forest nurseries for Pinus nigra. Laboratory experiments (adsorption–desorption isotherms, leaching experiment and degradation study) were carried out to determine possible mechanisms of dissipation. Higher adsorption was observed for hexazinone in Toledo ( K fT=0.69) compare to in Burgos soil ( K fB=0.20) probably due to the higher organic matter (OM) content of Toledo soil. No differences in adsorption were obtained for simazine in both soils ( K fT=1.27; K fB=1.34). In every case, adsorption was higher for simazine than for hexazinone, in both soils. The total recovery of hexazinone in the leachates from handpacked soil columns was higher in Burgos (100%) than in Toledo (80%), because of the larger adsorption of hexazinone in this last soil. No differences in simazine leaching between both soils were found, although the total amount of pesticide recovered in leachates (40% in the two soils) was lower for simazine than for hexazinone. Finally, lower degradation was found in Burgos ( t 1/2=91 d) vs Toledo ( t 1/2=47 d), directly related with the high OM content of Toledo. No half-life was calculated for simazine in Toledo because no changes in herbicide soil content were observed during the period of time studied. In the case of Burgos, the half-life for simazine was 50 days. The field residues study showed larger persistence of simazine than hexazinone mainly due to the higher adsorption and lower mobility of simazine in the two soils. The lower persistence of hexazinone in Toledo soil than in Burgos soil is related to the larger rainfall occurred in this soil besides the higher degradation of this herbicide observed in Toledo soil. The much lower temperature in Burgos than in Toledo soil during winter contribute to the higher persistence of the two herbicides in Burgos soil.

Leaching of simazine in organic‐amended soils

A laboratory study with a 1×3 factorial design has been conducted to assess the effect of the addition of 10% and 20% w/w of an organic amendment [26% organic carbon (C)] in sorption, degradation and leaching of simazine in a sandy soil (0.66% organic C, 75% sand, 16% clay). Sorption studies have been performed following a batch equilibration procedure and sorption isotherms fitted to Freundlich equation. The Kf increased by a factor of 2.5 and 1.8 with high and low amendment dose, respectively. Simazine treated soils were incubated at ‐33 KPa moisture content and 20°C for 28 days (d). Soils were sampled periodically and simazine residues extracted with methanol. No changes in simazine residues with incubation time were observed for the original unamended soil, whereas calculated half‐lives obtained by fitting simazine dissipation curves in the amended soils to first order kinetics were 123 d for the lower dose and 69 d for the high dose. Mobility was studied in handpacked soil columns under fluctuating saturated/ unsaturated flow conditions. Breakthrough curves were consistent with an inverse relationship between leaching and sorption, with greater mobility of simazine in the untreated sandy soil than in the amended soils. Recoveries of initially applied simazine in leachates after the application of 750 mL of water were 93% for the original soil, 88% for soil amended with the low dose of humic amendment, and 53% for the high dose, which is also consistent with degradation studies. These results indicate that the humic amendment reduces herbicide leaching by promoting sorption and degradation processes.

Dissipation of Simazine from the Soil

Dissipation of Simazine from the Soil