【1】Toxic substance will be left behind by using these facilities.（错误）

解析：错误的原因是因为没有弄清楚短语“leave sb/sth behind”准确含义

主动：leave sb/sth=leave behind sb sth

被动：=sb/sth be left behind主要有以下几个意思

(1)永久离开某人/抛下某人

Many of the women had left their husbands behind and they told of their fears that they may never see them again. 

这些女人中很多抛下了自己的丈夫，她们说害怕可能永远都见不到他们了。

(2)永久离开某地

We hear of women who run away, leaving behind their homes and families.  

我们听说有女人离家出走，扔下了家人不管。

"I'd go and live there and leave Kentucky behind," says Brown. 

“我要去那里生活，永远离开肯塔基州”，布朗说道。

(3)留下某物/余留某物

I don't want to leave anything behind.

我不想留下任何东西。

What do we humans leave behind? 

我们人类又能留下什么呢？

A misty rain in the morning had left behind a coolness that would stay for hours.  

早上，蒙蒙细雨带来一股清凉之意，数小时不散。

(4)把…抛在后面；超过

We're going to be left behind by the rest of the world. 

我们将被全世界甩在后面。

I got left behind at school with the maths. 

在校时我的数学跟不上。

Inflation has left them way behind. 

通货膨胀使他们远远落后了。

People are concerned about getting left behind right now. 
人们现在非常担心被落下。

根据以上情况我们可以把以上句子可以改为以下几种

(1)Toxic substance will be left behind after people use these facility.

(2) Toxic substance will be left behind if people use these facility.

(3) People will leave toxic substance behind (by) using these facilities.

(4)People’s using  these facilities will leave toxic substance behind. 

【2】Toxic substance will be left behind by people/people's using these facilities.（错误）

解析：以上错误是因为没有分清楚介词by/of区别，介词of后面动名词可以加逻辑主语，介词by不能加逻辑主语。

I insist on both of them coming in time.

我坚持要他们两人准时来。

I had not heard of your being ill. 

我没听说你病了。

Is there any hope of your workshop winning the red banner?

你们车间有希望获得红旗吗？

备注：以上都是介词of后面接动名词复合结构。

第2个也应该修改为上面4种结构中任何一种。