Pesticide traces in local crops of Sancti Spíritus, Cuba: risk assessment study

Background

Vegetables and rice produced in Cuba may contain residue of pesticides that exceed the maximum residue limits (MRLs). Pesticide residues on crop samples from Sancti Spíritus province were analyzed. Based on these residue data, a risk assessment of consumer exposure was conducted.

Methods

Samples collected during the 2017, 2018, and 2019 periods were analyzed using UPLC-MS/MS and GC/ECD chromatography techniques. A deterministic risk assessment was performed, using consumption data collected by the authors. Also, a probabilistic risk assessment was worked out with @RISK for the Monte Carlo simulation.

Results

A broad range of pesticides were detected in the samples. Most of the detected active ingredients were insecticides and fungicides. A considerable part of the detected pesticide residues exceeded the EU and Cuban MRLs. However, the deterministic risk assessment revealed that the consumer risk of pesticide exposure is low. Only in the maximum exposure scenario children and adults were exposed to methamidophos residues in tomatoes higher than the acceptable daily intake.

Conclusions

When a more realistic consumption (50th percentile) and higher (95th percentile) consumption pattern for tomatoes was assumed, the deterministic risk assessment found no chronic risk for children and adults being exposed to methamidophos present in the tomato samples. Furthermore, the probabilistic risk assessment concerning methamidophos exposure in tomato for children and adult strata showed no risk. To perform in the future a more accurate risk assessment for Cuban consumers it is important to have more detailed consumption data and an expanded dataset of the residues in different crops.

Pesticides residues in tobacco smoke: risk assessment study

Pesticides are not only used on food but also on non-food crops, such as tobacco, to control a range of unwanted animal, plant, and microbial, fungal pests. The residue levels in tobacco leaves are expected to decline up to harvest, during drying, and when the leaves are further processed. Additional pesticides may also be applied to the finished product and residue levels may remain present even when the tobacco is burned. Human exposure to pesticide residues on tobacco occurs when residues remaining in cigarette smoke are inhaled. Based on this assumption, the objectives of this research were (i) to determine the level of pesticides residues in harvested tobacco leaves and (ii) to assess the risk of human exposure to these residues in tobacco smoke. Pesticide residues were detected in all analysed tobacco samples. These detected residues represent ten different active ingredients (AI), three of these AIs (thiodicarb, alachlor, and endosulfan) are no longer allowed in Europe. A 54.7% of these residues were quantifiable. Furthermore, it was found that with the use of solid-phase extraction sorbent (SPE) as adsorbent and n-hexane as solvent, higher recoveries of the pesticide residues in the tobacco smoke from the amount spiked can be obtained. It was also found that cigarette filters help to reduce the intake of residues of pesticides that may be present in cigarettes. Finally, the study concluded that both active smoking and passive smoking populations are exposed to pesticide residues in the tobacco smoke.

Energetic, economic and environmental assessment for the anaerobic digestion of pretreated and codigested press mud

This study investigates the feasibility of anaerobic digestion (AD) of press mud previously pretreated, using two methods: Liquid Hot Water (LHW) and Thermo-Alkaline (TA), from an economic, energetic and environmental point of view. Two scenarios, a sugar mill with and without distillery were studied, considering monodigestion and vinasse codigestion. The results have shown that the LHW and TA pretreatments are self-sufficient in terms of thermal requirements since they can recover heat from the biogas engine, but the maximum electric and thermal net energy (64 MWh d^-1 and 95 MWh d^-1, respectively) was obtained during co-digestion with vinasse. The results of the environmental Life Cycle Analysis (LCA) show that the alternatives improve the environmental profiles, in both scenarios. The endpoint impact category "Human health" had the highest contribution because of both: the burning of fossil fuel at refinery to supply the required electricity; and the production of Ca(OH)₂ when vinasse was fed. The AD of pretreated press mud by LHW in CSTR reactors was the most viable for the scenario of a sugar mill without distillery, while the alternative co-digestion with the vinasse of the press mud without pretreatment was the most viable for the scenario of a sugar mill with distillery. This research shows that both the environmental and energetic profiles and the profitability of methane production can improve when the pretreatment and co-digestion of these wastes from the sugar - alcohol production process are considered.

Anaerobic co-digestion of sugarcane press mud with vinasse on methane yield

The conversion efficiency of high solids waste digestion as sugarcane press mud (P) may be limited due to hydrolysis step. The option of co-digestion with vinasse, main liquid waste generated from ethanol production, was investigated under batch regime at mesophilic conditions (37.5±1°C) and the best mixture was evaluated under semicontinuous regime in stirred-tank reactors. The maximum values for methane yield in batch tests were for V₇₅/P₂₅ and V₅₀/P₅₀ mixtures (on basis of the chemical oxygen demand (COD) percentage added in the mixture), with an average value of 246NmL CH₄g^-1 COD_fed, which was 13% higher than that of press mud alone. A highest methane production rate of 69.6NmL CH₄g^-1 COD_fed^-1d^-1 was obtained for the mixtureV₇₅/P₂₅. During the experiment carried out in CSTR reactors, the organic loading rate (OLR) was increased from 0.5 up to 2.2gVSL^-1d^-1. Methane yields of 365L CH₄ kg^-1VS and biogas productivities of 1.6LL^-1 were obtained in co-digestion, which was 64% higher in comparison to mono-digestion. The performance of the process in mono-digestion was less stable than in co-digestion, with a significant fall of methane yield to 1.8kgVSm^-3d^-1, and a partial inhibition of the methanogenic archaeas when the OLR was increased up to 2.2kgVSm^-3d^-1. The co-digestion of vinasse with press mud is a good option for the treatment of streams at the alcohol-sugar industry.

Thermo-chemical pre-treatment to solubilize and improve anaerobic biodegradability of press mud

Different pre-treatment severities by thermo-alkaline conditions (100°C, Ca(OH)2) on press mud were evaluated for different pre-treatment time and lime loading. COD solubilization and the methane yield enhancement were assessed. The biochemical methane potential was determined in batch assays under mesophilic conditions (37±1°C). The best pre-treatment resulted in a surplus of 72% of methane yield, adding 10g Ca(OH)2 100g(-1)TS(-1) for 1h. Pre-treatment also increased the COD solubilization, but the optimal severity for COD solubilization as determined by response surface methodology did not ensure the highest methane production. Inhibitory effects on anaerobic digestion were noticed when the severity was increased. These results demonstrate the relevance of thermo-alkaline pre-treatment severity in terms of both lime loading and pre-treatment time to obtain optimal anaerobic biodegradability of lignocellulosic biomass from press mud.