Mixture Toxicity of Bensulfuron-Methyl and Acetochlor to Red Swamp Crayfish (Procambarus clarkii): Behavioral, Morphological and Histological Effects

Abstract

The mixture of bensulfuron-methyl and acetochlor (MBA) has been widely applied as a rice herbicide in China, but the mixture toxicity of MBA to aquatic organisms is largely unknown. The current study aims to investigate the acute effects of MBA to juvenile red swamp crayfish, Procambarus clarkii. Firstly, a 96 h semi-static exposure was conducted to determine the Lethal Concentration 50 (LC50) values at 24, 48, 72 and 96 h, as well as to assess the behavioral and morphological effects. A second 96 h exposure was conducted at an MBA concentration of 50% of the 96 h LC50 (72.62 mg/L) to assess the histological changes in the gill, perigastric organ, muscle, heart, stomach, and midgut. The results showed that MBA exhibited low acute toxicity with the 24, 48, 72 and 96 h LC50 values of 191.25 (179.37–215.75), 166.81 (159.49–176.55), 154.30 (148.36–160.59) and 145.24 (138.94–151.27) mg/L, respectively. MBA-exposed crayfish showed body jerk, belly arch, equilibrium loss, body and appendage sway, and lethargy; and the dead crayfish showed dark gray or grayish-white body color and separated cephalothorax and abdomen. At 72.62 mg/L, MBA exposure caused significant histopathological alterations, mainly including the cuticular and epithelial degeneration of all the gills; atrophy of tubule lumina and cellular vacuolation of the perigastric organs (61.15 ± 9.90% of the tubules showed lesions); epithelial hyperplasia (48.40 ± 9.00%), myocardial fibers and epithelial cell lysis (17.30 ± 2.01%), and hemocytic infiltration of the hearts; cuticular swelling (15.82 ± 2.98%) and vacuolate connective tissue (11.30 ± 2.47%) of the stomachs; atrophied bladder cell and fragmented longitudinal muscles (95.23 ± 4.77%) of the midguts; and slight myofibers fragmentation and lysis (7.37 ± 0.53%) of the abdominal muscles. Our results indicate that MBA can cause behavioral, morphological and histopathological effects on juvenile P. clarkii at relatively high concentrations, but its acute toxicity is low compared with many other common herbicides.

Acute Toxicity of an Emerging Insecticide Pymetrozine to Procambarus clarkii Associated with Rice-Crayfish Culture (RCIS)

“…Juvenile P. clarkii were supplied by a crayfish breed cooperative in Qianjiang City, Hubei Province, China. Crayfish were transported to the laboratory of Institute of Hydrobiology, Chinese Academy of Sciences, and acclimated for 14 days, according to Yu et al [ 6 ]. Mortality during acclimation was below 5%.…”

“…Behavioral changes and mortality of the crayfish were recorded at 1, 12, 24, 48, 72 and 96 h after the introduction. Death was defined as lack of any movement of a crayfish within 5 min when probed gently with a glass rod, and dead crayfish were removed from the tanks [ 6 ].…”

“…Sections of 4 μm were prepared and stained with hematoxylin-eosin (H&E) [ 22 ]. An OLYMPUS BX53 microscope (Olympus Corporation, Tokyo, Japan) was used to examine the sections, and the histological impacts were quantified by measuring the percentages of different lesions’ area, number or length in three sections as repeats ( N = 3) [ 6 ].…”

“…The red swamp crayfish, Procambarus clarkii , is a widely-distributed freshwater crayfish and key species in many water bodies, and has great influences on the ecosystems, such as water quality, sediment, food web, and biodiversity [ 1 , 2 , 3 ]. P. clarkii has been widely used in water quality and pollution determination as a model organism [ 4 , 5 , 6 ].…”

“…Misuse of pyrethroids [ 10 ] and fipronil [ 12 ] has been reported to cause severe crayfish kills in RCIS. The non-target crayfish in rice fields may be poisoned by rice pesticide application, and in other water bodies by pesticide through drainage, migration of spray, surface runoff and even food chain [ 6 , 10 ].…”