Aquatic mesocosm assessments of a neem (azadirachtin) insecticide at environmentally realistic concentrations--2: zooplankton community responses and recovery

Alterations to unionid transformation during agricultural and urban contaminants of emerging concern exposures

Highly imperiled unionids have a complex life cycle including the metamorphosis of an obligate parasite life stage, larval glochidia, to the juvenile stage. Despite the known vulnerabilities of both glochidia and juveniles to pollutants, little is known on how metamorphosis success may be affected by chemical stress. Disruption of the transformation process in which glochidia encyst on the gills of a host fish, could lead to lowered recruitment and population declines. Transformation rates of Lampsilis cardium on host fish Micropterus salmoides were empirically derived from experimental exposures to low, medium, or high concentrations of an agricultural or urban mixture of contaminants of emerging concern (CECs) over two exposure durations. Transformation was characterized by: (1) a zero-inflated Poisson general linear mixed effects model to compare difference in transformation between exposure durations and (2) time response curves to describe the transformation curve using long-term exposure data. Lampsilis cardium transformation was similar between exposure durations. When compared to controls, CEC stress significantly reduced juvenile production (p « 0.05) except for the agricultural medium treatment and tended to increased encapsulation duration which while statistically insignificant (p = 0.16) may have ecological relevancy. Combining the empirically derived reduction of transformation rates with parameters values from the literature, a Lefkovich stage-based population model predicted strong declines in population size of L. cardium for all treatments if these results hold in nature. Management focus on urban CECs may lead to best conservation efforts though agricultural CECs may also have a concentration dependent impact on transformation and therefore overall recruitment and conservation success.

Effect of rainfall runoff from agricultural areas and seasonal crop practices on zooplankton community in Pampean streams, Argentina

Extreme climatic events are considered one of the main consequences of climate change. In the Pampas region, Argentina, an intensification of rainfall is expected during the periods of maximum agrochemical application. This study assesses the main factors determining the zooplankton community attributes in three streams belonging to the agricultural Pampas region, Argentina, and the effect of rainfall and seasonal crop practices on the zooplankton community composition. Sampling campaigns were performed before and after three rainfall events during two seasonal crop practices: (1) soybean chemical fallow-sowing and corn vegetative growth-flowering, (2) soybean vegetative growth-grain filling and corn sowing. The runoff in agricultural areas affected the zooplankton community attributes and composition. The biological oxygen demand, turbidity, and conductivity were the main water quality variables affecting the zooplankton community attributes. The increase of these variables after rainfall or during pre-emergence crop practices favoured the zooplankton groups most tolerant to eutrophication such as Bdelloidea, Chydoridae, Moinidae, and Sididae. Factors such as rainfall and seasonal crop practices must be considered in environmental monitoring design.

Non-target toxicity of novel insecticides

Humans have used insecticides since ancient times. The spectrum and potency of available insecticidal substances has greatly expanded since the industrial revolution, resulting in widespread use and unforeseen levels of synthetic chemicals in the environment. Concerns about the toxic effects of these new chemicals on non-target species became public soon after their appearance, which eventually led to the restrictions of use. At the same time, new, more environmentally-friendly insecticides have been developed, based on naturally occurring chemicals, such as pyrethroids (derivatives of pyrethrin), neonicotinoids (derivatives of nicotine), and insecticides based on the neem tree vegetable oil (Azadirachta indica), predominantly azadirachtin. Although these new substances are more selective toward pest insects, they can still target other organisms. Neonicotinoids, for example, have been implicated in the decline of the bee population worldwide. This review summarises recent literature published on non-target toxicity of neonicotinoids, pyrethroids, and neem-based insecticidal substances, with a special emphasis on neonicotinoid toxicity in honeybees. We also touch upon the effects of pesticide combinations and documented human exposure to these substances.

Azadirachtin, a neem-derived biopesticide, impairs behavioral and hematological parameters in carp (Cyprinus carpio)

Azadirachtin (Aza) is a promisor biopesticide used in organic production and aquaculture. Although this compound is apparently safe, there is evidence that it may have deleterious effects on fish. Behavioral and hematological tests are grouped into a set of parameters that may predict potential toxicity of chemical compounds. Here, we investigate the effects of Aza, in the commercial formulation Neenmax^™ , on carp (Cyprinus carpio) by defining LC₅₀ (96 h), and testing behavioral and hematological parameters. In our study, LC₅₀ was estimated at 80 μL/L. We exposed carp to Aza at 20, 40, and 60 μL/L, values based on 25, 50, and 75% of LC₅₀ , respectively. At 60 μL/L, Aza promoted significant changes in several parameters, increasing the distance traveled and absolute turn angle. In addition, the same concentration decreased the time spent immobile and the number of immobile episodes. Hematological parameters, such as hematocrit, hemoglobin, hematimetrics index, and red cell distribution, were decreased at 60 μL/L Aza exposure. In conclusion, our study demonstrates that 60 μL/L Aza altered locomotor activity, motor pattern, and hematological parameters, suggesting potential toxicity to carp after acute exposure. In addition, this is the first report that evaluates the actions of a chemical contaminant using automated behavioral tracking of carp, which may be a useful tool for assessing the potential toxicity of biopesticides in conjunction with hematological tests. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1381-1388, 2016.

Acute exposure to the biopesticide azadirachtin affects parameters in the gills of common carp (Cyprinus carpio)

The biopesticide, azadirachtin (Aza) is less hazardous to the environment, but may cause several toxic effects in aquatic organisms. The Cyprinus carpio (n=12, for all concentrations) after 10days of acclimation under controlled conditions, were exposed at 20, 40, and 60μL/L of Aza during 96h. After this period, fish were anesthetized and euthanized then mucus layer and gills collected. In this study, the effects of exposure to different Aza concentrations were analysed through a set of biomarkers: Na(+)/K(+-)ATPase, lipid peroxidation (TBARS), protein carbonyl (PC), superoxide dismutase (SOD), glutathione-S-transferase (GST), catalase (CAT), glutathione peroxidase (GPx), non-protein thiols (NPSH), ascorbic acid (AsA) and histological parameters and, yet, protein and glucose concentration in the surface area of mucous layer. Na(+)K(+-)ATPase was inhibited at 40 and 60μL/L compared to control. TBARS decreased at 40μL/L compared to control. PC, SOD and GST increased at 60μL/L in comparison to control. CAT increased at 20 and 60μL/L, and GPx increased in all Aza concentrations compared to control. NPSH decreased and AsA increased in all concentrations in comparison to control. Histological analyses demonstrated an increase in the intensity of the damage with increasing Aza concentration. Alterations in histological examination were elevation and hypertrophy of the epithelial cells of the secondary filament, hypertrophy and hyperplasia of the mucous and chlorate cells and lamellar aneurism. Glucose and protein concentrations in mucus layer increased at 60μL/L compared to control. In general, we suggest that 60μL/L Aza concentration affected several parameters causing disruptions carp metabolism.

Acute lethal and sublethal effects of neem leaf extract on the neotropical freshwater fish Prochilodus lineatus

The aim of this study was to determine the toxicity of the aqueous extract of neem leaves, a product extensively used in fish-farms as alternative for the control of fish parasites and fish fry predators, for the neotropical fish Prochilodus lineatus. The 24 h LC(50) of neem leaf extract for juveniles P. lineatus was estimated as 4.8 g L(-1); the fish were then exposed for 24 h to 2.5, 5.0 and 7.5 g L(-1) or only clean water (control). Plasma glucose levels were higher in fish exposed to 2.5 g L(-1) and 5.0 g L(-1) neem extract, relative to control, indicating a typical stress response. Neem extract did not interfere with the osmoregulating capacity of the fish, as their plasma sodium, chloride, total protein and osmolarity did not change. The presence of the biopesticide interfered with the antioxidant defense system of P. lineatus, as there was a decrease in liver catalase activity at all neem concentrations and the detoxifying enzyme glutathione-S-transferase was activated in fish exposed to 5.0 g L(-1). Fish exposed to all neem extract concentrations exhibited damaged gill and kidney tissue. These results indicate that although neem extract is less toxic to P. lineatus than other synthetic insecticides used in fish-farming it does cause functional and morphological changes in this fish species.

Atrazine effects on meiobenthic assemblages of a modular estuarine mesocosm

Atrazine is a widely used herbicide in the US found at levels ranging from <10 ng/L to 62.5 microg/L in estuaries throughout the southeast. Effects of atrazine on estuarine meiobenthic assemblages chronically exposed to environmentally relevant concentrations are unknown. The purpose of our research was to assess effects of atrazine on meiobenthos at concentrations near the proposed USEPA SWQC (26 microg/L) using modular estuarine salt marsh mesocosms as a field surrogate. Indigenous copepod and nematode densities were assessed after 28 days of exposure in transplanted colonization chambers. Cluster analysis showed a group characterized by low copepod densities, mostly atrazine exposed chambers, and a group containing all but one control chamber. The later group included chambers with high densities of the copepods Paronychocamptus wilsoni and Enhydrosoma baruchi. Compared to controls, copepod densities was approximately 70% lower in atrazine chambers, with three of the most common copepod species (E. baruchi, Onychocamptus sp. and P. wilsoni) showing an average of 50-70% reduction in population densities (p<0.05). Although nematode density did not differ between atrazine and control chambers, the nematode-to-copepod ratio was significantly higher in atrazine (9.95+/-7.61; p=0.011) than in control chambers (0.61+/-0.35). Our findings suggest that chronic exposures over multiple generations to atrazine at concentrations near the proposed USEPA SWQC could have significant effects on the abundance and composition of estuarine meiobenthic copepod assemblages.

Fate and effects of azadirachtin in aquatic mesocosms--1: fate in water and bottom sediments

The fate and effects of azadirachtin were examined using in situ enclosures deployed in a typical forest pond of northern Ontario. A commercial azadirachtin-based insecticide formulation, Neemix 4.5, was applied as the test substance. Fate studies were conducted to determine kinetics and persistence of azadirachtin isomers A and B in the aqueous phase and whether either isomer partitioned significantly to bottom sediments or pore water. Aqueous azadirachtin residues dissipated following slow linear kinetics with time to 50% dissipation of 25, 45, and 30 days for azadirachtin A, azadirachtin B, and total residues, respectively. Sediment pore water concentrations increased slowly, reaching low-level equilibrium with the overlying water column toward the end of the summer season. No significant sorption to bottom sediments was observed. Results demonstrated that fate and dissipation of azadirachtin residues are consistent from year to year and that biota may be chronically exposed to diminishing levels of azadirachtins A and B in aqueous phase under conditions of a typical forest pond environment.