Detect block

/scoreboard objectives add block dummy

/execute @p ~ ~-1 ~ fill ~ ~ ~ ~ ~ ~ cactus 0 replace sponge
/execute @p ~ ~-1 ~ fill ~1 ~ ~1 ~-1 ~ ~-1 barrier 0 replace air

/execute @e ~ ~ ~ scoreboard players set @e[type=Item,r=10] block 1 {Item:{id:minecraft:cactus}}
/execute @p ~ ~-1 ~ fill ~1 ~ ~1 ~-1 ~ ~-1 air 0 replace barrier

/execute @e[type=Item,score_block_min=1] ~ ~ ~ effect @p[r=4] 8 5 10

/execute @e[type=Item,score_block_min=1] ~ ~ ~ /setblock ~ ~ ~ sponge

/kill @e[type=Item,score_block_min=1]